diff --git a/backend/.env.example b/backend/.env.example
index 545c4b0..1e6a24b 100644
--- a/backend/.env.example
+++ b/backend/.env.example
@@ -11,6 +11,13 @@ AIS_API_KEY=              # https://aisstream.io/ — free tier WebSocket key
 
 # ── Optional ───────────────────────────────────────────────────
 
+# AISHub REST fallback. Used when stream.aisstream.io is unreachable
+# (e.g. their cert expires or server goes offline). Free tier requires
+# registration at https://www.aishub.net/api. Poll cadence defaults to
+# 20 min to stay courteous; tunable via AISHUB_POLL_INTERVAL_MINUTES.
+# AISHUB_USERNAME=
+# AISHUB_POLL_INTERVAL_MINUTES=20
+
 # Override allowed CORS origins (comma-separated). Defaults to localhost + LAN auto-detect.
 # CORS_ORIGINS=http://192.168.1.50:3000,https://my-domain.com
 
diff --git a/backend/services/data_fetcher.py b/backend/services/data_fetcher.py
index bdbefb0..65bb8f7 100644
--- a/backend/services/data_fetcher.py
+++ b/backend/services/data_fetcher.py
@@ -777,6 +777,26 @@ def start_scheduler():
         misfire_grace_time=60,
     )
 
+    # AISHub REST fallback — slow polling when the AISStream WebSocket
+    # primary is offline. Configurable interval via
+    # AISHUB_POLL_INTERVAL_MINUTES env (default 20 min). Operator must
+    # set AISHUB_USERNAME to opt in. The fetcher is gated internally on
+    # the primary being disconnected, so this job is cheap when the
+    # WebSocket is healthy (early-returns after a status check).
+    from services.fetchers.aishub_fallback import (
+        aishub_poll_interval_minutes,
+        fetch_aishub_vessels,
+    )
+    _aishub_interval = aishub_poll_interval_minutes()
+    _scheduler.add_job(
+        lambda: _run_task_with_health(fetch_aishub_vessels, "fetch_aishub_vessels"),
+        "interval",
+        minutes=_aishub_interval,
+        id="aishub_fallback",
+        max_instances=1,
+        misfire_grace_time=120,
+    )
+
     # Route database — bulk refresh from vrs-standing-data.adsb.lol every 5
     # days. Replaces the legacy /api/0/routeset POST (blocked under our UA,
     # and broken upstream). Airline schedules change on a quarterly cycle,
diff --git a/backend/services/fetchers/aishub_fallback.py b/backend/services/fetchers/aishub_fallback.py
new file mode 100644
index 0000000..b8d51b0
--- /dev/null
+++ b/backend/services/fetchers/aishub_fallback.py
@@ -0,0 +1,290 @@
+"""AISHub REST fallback for ship tracking when AISStream is unreachable.
+
+Background
+----------
+On 2026-05-23 ``stream.aisstream.io`` (the primary live AIS WebSocket feed)
+went fully offline. Backend's only ship signal vanished. This module polls
+``data.aishub.net``'s free REST API on a slow cadence (default 20 min) when
+the WebSocket primary is disconnected, so the ships layer doesn't go fully
+dark during upstream outages.
+
+Why 20 minutes
+--------------
+AISHub's free tier is rate-limited and explicitly asks consumers to be
+courteous. 20 minutes is well inside their limits, gives ships time to
+move enough to look "alive" on the map, and won't drain their service.
+Configurable via the ``AISHUB_POLL_INTERVAL_MINUTES`` env var (clamped to
+[1, 360]).
+
+Why slow vs primary
+-------------------
+This is degraded mode, not a replacement. A ship at 20 knots moves about
+6 nautical miles in 20 minutes — visible on the map but coarser than the
+real-time WebSocket signal. When AISStream comes back online, the
+WebSocket data will overwrite these records via the same ``_vessels``
+dict and ``source`` will flip from ``"aishub"`` back to upstream-live.
+
+Opt-in
+------
+Operator must set ``AISHUB_USERNAME`` (free registration at
+https://www.aishub.net/api). If unset, this fetcher is a no-op.
+"""
+
+from __future__ import annotations
+
+import json
+import logging
+import os
+import time
+from typing import Any
+
+from services.network_utils import fetch_with_curl
+
+logger = logging.getLogger(__name__)
+
+
+AISHUB_URL = "https://data.aishub.net/ws.php"
+
+
+def aishub_username() -> str:
+    return str(os.environ.get("AISHUB_USERNAME", "")).strip()
+
+
+def aishub_fallback_enabled() -> bool:
+    """Returns True only when the operator has registered with AISHub and
+    set ``AISHUB_USERNAME``. The presence of the username is the opt-in."""
+    return bool(aishub_username())
+
+
+def aishub_poll_interval_minutes() -> int:
+    """Default 20 minutes. Clamped to [1, 360] so a hostile or
+    misconfigured env var can't either hammer the upstream or silence the
+    fallback for a day."""
+    raw = os.environ.get("AISHUB_POLL_INTERVAL_MINUTES", "20")
+    try:
+        value = int(str(raw).strip())
+    except (TypeError, ValueError):
+        value = 20
+    return max(1, min(360, value))
+
+
+def _should_run_fallback() -> bool:
+    """Only run when the primary WebSocket is disconnected. Avoids stomping
+    over fresher live data when AISStream is healthy.
+
+    Returns False if:
+      * AISHub isn't configured (no username)
+      * AISStream primary is currently connected (recent vessel messages)
+
+    Returns True only when AIS is configured-but-down. The
+    ``proxy_spawn_count > 0`` guard means "the primary has at least tried
+    to run" — if the user set AISHUB_USERNAME but not AIS_API_KEY at all,
+    AISHub will still serve as a primary on its own slow cadence.
+    """
+    if not aishub_fallback_enabled():
+        return False
+    try:
+        from services.ais_stream import ais_proxy_status
+        status = ais_proxy_status() or {}
+    except Exception:
+        return True  # ais_stream not importable? still try AISHub.
+    # If the WebSocket primary is connected, skip the fallback — fresher
+    # data is already flowing.
+    if status.get("connected") is True:
+        return False
+    return True
+
+
+def _parse_aishub_response(payload: str) -> list[dict]:
+    """Parse the AISHub JSON response into a list of vessel records.
+
+    Successful response shape::
+
+        [
+            {"ERROR": false, "USERNAME": "...", "FORMAT": "1", "RECORDS": N},
+            [{"MMSI": ..., "LATITUDE": ..., "LONGITUDE": ..., ...}, ...]
+        ]
+
+    Error response shape::
+
+        [{"ERROR": true, "ERROR_MESSAGE": "..."}]
+
+    Empty payload (e.g. silent rate-limit drop) returns ``[]``.
+    """
+    if not payload or not payload.strip():
+        return []
+    try:
+        data = json.loads(payload)
+    except json.JSONDecodeError as e:
+        logger.warning("AISHub: response is not JSON: %s", e)
+        return []
+    if not isinstance(data, list) or not data:
+        return []
+    header = data[0] if isinstance(data[0], dict) else {}
+    if header.get("ERROR") is True:
+        logger.warning(
+            "AISHub: upstream error: %s",
+            header.get("ERROR_MESSAGE", "<unspecified>"),
+        )
+        return []
+    if len(data) < 2 or not isinstance(data[1], list):
+        return []
+    return [row for row in data[1] if isinstance(row, dict)]
+
+
+def _normalize_record(row: dict) -> dict | None:
+    """Map an AISHub vessel record to our internal vessel schema.
+
+    Returns None when the record can't be used (no MMSI, bad position,
+    sentinel "not available" lat/lng).
+    """
+    try:
+        mmsi = int(row.get("MMSI") or 0)
+    except (TypeError, ValueError):
+        return None
+    if not mmsi:
+        return None
+    try:
+        lat = float(row.get("LATITUDE"))
+        lng = float(row.get("LONGITUDE"))
+    except (TypeError, ValueError):
+        return None
+    # AIS uses 91/181 as "no position available" sentinels.
+    if abs(lat) > 90 or abs(lng) > 180:
+        return None
+    if lat == 91.0 or lng == 181.0:
+        return None
+    # SOG raw 102.3 is "speed not available"; sanitize to 0.
+    try:
+        sog_raw = float(row.get("SOG") or 0)
+    except (TypeError, ValueError):
+        sog_raw = 0.0
+    sog = 0.0 if sog_raw >= 102.2 else sog_raw
+    try:
+        cog = float(row.get("COG") or 0)
+    except (TypeError, ValueError):
+        cog = 0.0
+    try:
+        heading_raw = int(row.get("HEADING") or 511)
+    except (TypeError, ValueError):
+        heading_raw = 511
+    # AIS heading sentinel 511 = "not available" — fall back to COG.
+    heading = heading_raw if heading_raw != 511 else cog
+    try:
+        ais_type = int(row.get("TYPE") or 0)
+    except (TypeError, ValueError):
+        ais_type = 0
+    return {
+        "mmsi": mmsi,
+        "lat": lat,
+        "lng": lng,
+        "sog": sog,
+        "cog": cog,
+        "heading": heading,
+        "name": str(row.get("NAME") or "").strip() or "UNKNOWN",
+        "callsign": str(row.get("CALLSIGN") or "").strip(),
+        "destination": str(row.get("DEST") or "").strip().replace("@", "") or "",
+        "imo": int(row.get("IMO") or 0),
+        "ais_type_code": ais_type,
+    }
+
+
+def fetch_aishub_vessels() -> int:
+    """Poll AISHub and merge vessels into the shared ``_vessels`` store.
+
+    Returns the number of vessels updated (0 on skip, error, or no data).
+    Designed to be called by the APScheduler tier — see
+    ``data_fetcher.py`` for the 20-minute interval job that wraps this.
+    """
+    if not _should_run_fallback():
+        logger.debug("AISHub fallback skipped: primary connected or not configured")
+        return 0
+
+    username = aishub_username()
+    url = (
+        f"{AISHUB_URL}?username={username}&format=1&output=json"
+        f"&compress=0"
+    )
+
+    try:
+        response = fetch_with_curl(url, timeout=30)
+    except Exception as e:
+        logger.warning("AISHub fetch failed: %s", e)
+        return 0
+
+    if not response or response.status_code != 200:
+        logger.warning(
+            "AISHub HTTP %s",
+            getattr(response, "status_code", "None"),
+        )
+        return 0
+
+    rows = _parse_aishub_response(getattr(response, "text", "") or "")
+    if not rows:
+        return 0
+
+    # Inline imports to avoid a circular dependency at module load time
+    # (ais_stream imports lots of things and is loaded by main.py).
+    from services.ais_stream import (
+        _vessels,
+        _vessels_lock,
+        _record_vessel_trail_locked,
+        classify_vessel,
+        get_country_from_mmsi,
+    )
+
+    now = time.time()
+    count = 0
+    with _vessels_lock:
+        for row in rows:
+            normalized = _normalize_record(row)
+            if normalized is None:
+                continue
+            mmsi = normalized["mmsi"]
+            vessel = _vessels.setdefault(mmsi, {"mmsi": mmsi})
+            # Don't overwrite fresher live data: if the WebSocket pushed an
+            # update for this MMSI more recently than now-1s (race during
+            # the brief reconnection window) keep the live one.
+            last = float(vessel.get("_updated") or 0)
+            if last > now - 1:
+                continue
+            vessel.update(
+                {
+                    "lat": normalized["lat"],
+                    "lng": normalized["lng"],
+                    "sog": normalized["sog"],
+                    "cog": normalized["cog"],
+                    "heading": normalized["heading"],
+                    "_updated": now,
+                    "source": "aishub",
+                }
+            )
+            if normalized["name"] and normalized["name"] != "UNKNOWN":
+                vessel["name"] = normalized["name"]
+            if normalized["callsign"]:
+                vessel["callsign"] = normalized["callsign"]
+            if normalized["destination"]:
+                vessel["destination"] = normalized["destination"]
+            if normalized["imo"]:
+                vessel["imo"] = normalized["imo"]
+            if normalized["ais_type_code"]:
+                vessel["ais_type_code"] = normalized["ais_type_code"]
+                vessel["type"] = classify_vessel(normalized["ais_type_code"], mmsi)
+            if not vessel.get("country"):
+                vessel["country"] = get_country_from_mmsi(mmsi)
+            _record_vessel_trail_locked(
+                mmsi,
+                normalized["lat"],
+                normalized["lng"],
+                normalized["sog"],
+                now,
+            )
+            count += 1
+
+    if count:
+        logger.info(
+            "AISHub fallback: merged %d vessels (poll interval %d min)",
+            count,
+            aishub_poll_interval_minutes(),
+        )
+    return count
diff --git a/backend/tests/test_aishub_fallback.py b/backend/tests/test_aishub_fallback.py
new file mode 100644
index 0000000..4cf1083
--- /dev/null
+++ b/backend/tests/test_aishub_fallback.py
@@ -0,0 +1,432 @@
+"""AISHub REST fallback for ship tracking.
+
+Background
+----------
+When ``stream.aisstream.io`` (the WebSocket primary) is unreachable, the
+ships layer goes empty. ``aishub_fallback.py`` polls ``data.aishub.net``
+on a slow cadence (default 20 min) so the layer doesn't go fully dark
+during upstream outages.
+
+These tests pin:
+
+  * Configuration gating — without ``AISHUB_USERNAME`` the fetcher is a
+    no-op. The username's presence is the opt-in.
+  * Connectivity gating — when the WebSocket primary is connected, the
+    fallback skips so it doesn't stomp fresher live data.
+  * Response parsing — successful, error, and empty AISHub payloads.
+  * Record normalization — bad records (no MMSI, sentinel positions) are
+    dropped without crashing.
+  * Merge behavior — records land in the shared ``_vessels`` dict with
+    ``source: "aishub"`` and don't overwrite very-recent live updates.
+  * Poll interval clamping — env var overrides honored within [1, 360].
+"""
+
+from __future__ import annotations
+
+import json
+import os
+import time
+
+import pytest
+
+
+# ---------------------------------------------------------------------------
+# Configuration / gating
+# ---------------------------------------------------------------------------
+
+
+class TestGating:
+    def test_no_username_means_disabled(self, monkeypatch):
+        from services.fetchers.aishub_fallback import (
+            aishub_fallback_enabled,
+            fetch_aishub_vessels,
+        )
+        monkeypatch.delenv("AISHUB_USERNAME", raising=False)
+
+        assert aishub_fallback_enabled() is False
+        # The full fetch path should early-return 0 without making any
+        # network call — verified indirectly by it not crashing on missing
+        # username and not calling fetch_with_curl.
+        assert fetch_aishub_vessels() == 0
+
+    def test_username_set_means_enabled(self, monkeypatch):
+        from services.fetchers.aishub_fallback import aishub_fallback_enabled
+        monkeypatch.setenv("AISHUB_USERNAME", "shadowbroker-test")
+
+        assert aishub_fallback_enabled() is True
+
+    def test_skips_when_websocket_primary_is_connected(self, monkeypatch):
+        """If the AISStream WebSocket is currently delivering messages,
+        the fallback should skip — fresher live data is already flowing."""
+        from services.fetchers import aishub_fallback
+        from services import ais_stream as ais
+
+        monkeypatch.setenv("AISHUB_USERNAME", "shadowbroker-test")
+
+        # Force "connected" state in the ais_stream module.
+        with ais._vessels_lock:
+            ais._last_msg_at = time.time() - 5  # 5s ago — well inside 60s
+            ais._proxy_spawn_count = 1
+        # Sanity check the gate:
+        assert ais.ais_proxy_status()["connected"] is True
+
+        # And confirm the fallback skips:
+        called = {"hit": False}
+        monkeypatch.setattr(
+            aishub_fallback,
+            "fetch_with_curl",
+            lambda *a, **kw: (_ for _ in ()).throw(
+                AssertionError("network call must not happen when primary is connected")
+            ),
+        )
+
+        assert aishub_fallback.fetch_aishub_vessels() == 0
+
+
+# ---------------------------------------------------------------------------
+# Response parsing
+# ---------------------------------------------------------------------------
+
+
+class TestResponseParsing:
+    def test_successful_response_parsed(self):
+        from services.fetchers.aishub_fallback import _parse_aishub_response
+
+        payload = json.dumps([
+            {"ERROR": False, "USERNAME": "test", "FORMAT": "1", "RECORDS": 2},
+            [
+                {"MMSI": 123, "LATITUDE": 40.0, "LONGITUDE": -73.0},
+                {"MMSI": 456, "LATITUDE": 51.5, "LONGITUDE": -0.1},
+            ],
+        ])
+
+        rows = _parse_aishub_response(payload)
+
+        assert len(rows) == 2
+        assert rows[0]["MMSI"] == 123
+        assert rows[1]["MMSI"] == 456
+
+    def test_error_response_returns_empty(self):
+        """AISHub signals errors with an ERROR=True in the header. We log
+        and treat as no data."""
+        from services.fetchers.aishub_fallback import _parse_aishub_response
+
+        payload = json.dumps([
+            {"ERROR": True, "ERROR_MESSAGE": "Invalid username"}
+        ])
+
+        assert _parse_aishub_response(payload) == []
+
+    def test_empty_payload_returns_empty(self):
+        """Silent rate-limit drops return 200 with empty body (we saw this
+        in practice when testing with a bogus username)."""
+        from services.fetchers.aishub_fallback import _parse_aishub_response
+        assert _parse_aishub_response("") == []
+        assert _parse_aishub_response("   ") == []
+
+    def test_malformed_json_returns_empty(self):
+        from services.fetchers.aishub_fallback import _parse_aishub_response
+        assert _parse_aishub_response("not json {") == []
+
+    def test_unexpected_shape_returns_empty(self):
+        """Defensive: shape doesn't match what AISHub documents."""
+        from services.fetchers.aishub_fallback import _parse_aishub_response
+        assert _parse_aishub_response(json.dumps({"unexpected": "object"})) == []
+        assert _parse_aishub_response(json.dumps([])) == []
+        # Header-only with no records list:
+        assert _parse_aishub_response(json.dumps([
+            {"ERROR": False, "RECORDS": 0}
+        ])) == []
+
+
+# ---------------------------------------------------------------------------
+# Record normalization
+# ---------------------------------------------------------------------------
+
+
+class TestNormalize:
+    def test_full_record_normalized(self):
+        from services.fetchers.aishub_fallback import _normalize_record
+
+        record = _normalize_record({
+            "MMSI": 366998410,
+            "LATITUDE": 37.8,
+            "LONGITUDE": -122.4,
+            "COG": 280,
+            "SOG": 12.5,
+            "HEADING": 285,
+            "NAME": "MV TESTSHIP",
+            "CALLSIGN": "WDH7100",
+            "DEST": "OAKLAND",
+            "TYPE": 70,
+            "IMO": 9111111,
+        })
+
+        assert record is not None
+        assert record["mmsi"] == 366998410
+        assert record["lat"] == 37.8
+        assert record["lng"] == -122.4
+        assert record["sog"] == 12.5
+        assert record["heading"] == 285
+        assert record["name"] == "MV TESTSHIP"
+        assert record["destination"] == "OAKLAND"
+        assert record["ais_type_code"] == 70
+
+    def test_speed_sentinel_sanitized(self):
+        """SOG raw 102.3+ kn = "speed not available" in the AIS spec.
+        Sanitize to 0 so it doesn't look like a 200-knot ship."""
+        from services.fetchers.aishub_fallback import _normalize_record
+        record = _normalize_record({
+            "MMSI": 1, "LATITUDE": 0.5, "LONGITUDE": 0.5,
+            "SOG": 102.3, "COG": 0,
+        })
+        assert record["sog"] == 0.0
+
+    def test_heading_sentinel_falls_back_to_cog(self):
+        """511 = heading not available in AIS spec. Use COG instead."""
+        from services.fetchers.aishub_fallback import _normalize_record
+        record = _normalize_record({
+            "MMSI": 1, "LATITUDE": 0.5, "LONGITUDE": 0.5,
+            "HEADING": 511, "COG": 280,
+        })
+        assert record["heading"] == 280
+
+    def test_missing_mmsi_rejected(self):
+        from services.fetchers.aishub_fallback import _normalize_record
+        assert _normalize_record({"LATITUDE": 0.5, "LONGITUDE": 0.5}) is None
+        assert _normalize_record({"MMSI": 0, "LATITUDE": 0.5, "LONGITUDE": 0.5}) is None
+
+    def test_no_position_rejected(self):
+        from services.fetchers.aishub_fallback import _normalize_record
+        assert _normalize_record({"MMSI": 1}) is None
+        assert _normalize_record({"MMSI": 1, "LATITUDE": 0.5}) is None
+        assert _normalize_record({"MMSI": 1, "LONGITUDE": 0.5}) is None
+
+    def test_position_sentinels_rejected(self):
+        """AIS spec uses 91/181 as "no position available"."""
+        from services.fetchers.aishub_fallback import _normalize_record
+        assert _normalize_record({
+            "MMSI": 1, "LATITUDE": 91.0, "LONGITUDE": 0.0
+        }) is None
+        assert _normalize_record({
+            "MMSI": 1, "LATITUDE": 0.0, "LONGITUDE": 181.0
+        }) is None
+
+    def test_out_of_range_rejected(self):
+        from services.fetchers.aishub_fallback import _normalize_record
+        assert _normalize_record({
+            "MMSI": 1, "LATITUDE": 95.0, "LONGITUDE": 0.0
+        }) is None
+        assert _normalize_record({
+            "MMSI": 1, "LATITUDE": 0.0, "LONGITUDE": 200.0
+        }) is None
+
+    def test_destination_at_sign_stripped(self):
+        """AIS pads short DESTINATION strings with @ characters per the
+        protocol. Strip them so the UI doesn't render "OAKLAND@@@@@"."""
+        from services.fetchers.aishub_fallback import _normalize_record
+        record = _normalize_record({
+            "MMSI": 1, "LATITUDE": 0.5, "LONGITUDE": 0.5,
+            "DEST": "OAKLAND@@@",
+        })
+        assert record["destination"] == "OAKLAND"
+
+
+# ---------------------------------------------------------------------------
+# Poll interval clamping
+# ---------------------------------------------------------------------------
+
+
+class TestPollInterval:
+    def test_default_is_twenty_minutes(self, monkeypatch):
+        from services.fetchers.aishub_fallback import aishub_poll_interval_minutes
+        monkeypatch.delenv("AISHUB_POLL_INTERVAL_MINUTES", raising=False)
+        assert aishub_poll_interval_minutes() == 20
+
+    def test_env_override_honored(self, monkeypatch):
+        from services.fetchers.aishub_fallback import aishub_poll_interval_minutes
+        monkeypatch.setenv("AISHUB_POLL_INTERVAL_MINUTES", "45")
+        assert aishub_poll_interval_minutes() == 45
+
+    def test_clamp_lower_bound(self, monkeypatch):
+        """A 0 or negative env var would hammer the upstream — clamp."""
+        from services.fetchers.aishub_fallback import aishub_poll_interval_minutes
+        monkeypatch.setenv("AISHUB_POLL_INTERVAL_MINUTES", "0")
+        assert aishub_poll_interval_minutes() == 1
+        monkeypatch.setenv("AISHUB_POLL_INTERVAL_MINUTES", "-5")
+        assert aishub_poll_interval_minutes() == 1
+
+    def test_clamp_upper_bound(self, monkeypatch):
+        """A 99999 env var would silence the fallback effectively forever."""
+        from services.fetchers.aishub_fallback import aishub_poll_interval_minutes
+        monkeypatch.setenv("AISHUB_POLL_INTERVAL_MINUTES", "99999")
+        assert aishub_poll_interval_minutes() == 360
+
+    def test_malformed_env_defaults(self, monkeypatch):
+        from services.fetchers.aishub_fallback import aishub_poll_interval_minutes
+        monkeypatch.setenv("AISHUB_POLL_INTERVAL_MINUTES", "twenty")
+        assert aishub_poll_interval_minutes() == 20
+
+
+# ---------------------------------------------------------------------------
+# End-to-end fetch + merge into _vessels store
+# ---------------------------------------------------------------------------
+
+
+class TestFetchAndMerge:
+    def _force_primary_disconnected(self):
+        """Set ais_stream module state so the gate allows the fallback."""
+        from services import ais_stream as ais
+        with ais._vessels_lock:
+            # Far in the past → connected = false; spawn_count > 0 → primary
+            # has at least tried so the gate engages.
+            ais._last_msg_at = time.time() - 3600
+            ais._proxy_spawn_count = 5
+            ais._vessels.clear()
+
+    def test_vessels_merged_with_source_tag(self, monkeypatch):
+        """Happy path: AISHub returns 2 ships, both land in ``_vessels``
+        with ``source: 'aishub'``."""
+        from services.fetchers import aishub_fallback
+        from services import ais_stream as ais
+
+        monkeypatch.setenv("AISHUB_USERNAME", "test-user")
+        self._force_primary_disconnected()
+
+        payload = json.dumps([
+            {"ERROR": False, "USERNAME": "test-user", "FORMAT": "1", "RECORDS": 2},
+            [
+                {
+                    "MMSI": 111111111,
+                    "LATITUDE": 40.0,
+                    "LONGITUDE": -73.0,
+                    "SOG": 12.0,
+                    "COG": 270,
+                    "HEADING": 275,
+                    "NAME": "SHIP A",
+                    "TYPE": 70,
+                },
+                {
+                    "MMSI": 222222222,
+                    "LATITUDE": 51.5,
+                    "LONGITUDE": -0.1,
+                    "SOG": 8.0,
+                    "COG": 90,
+                    "HEADING": 92,
+                    "NAME": "SHIP B",
+                    "TYPE": 60,
+                },
+            ],
+        ])
+
+        class FakeResp:
+            status_code = 200
+            text = payload
+
+        monkeypatch.setattr(
+            aishub_fallback, "fetch_with_curl", lambda *a, **kw: FakeResp()
+        )
+
+        count = aishub_fallback.fetch_aishub_vessels()
+
+        assert count == 2
+        with ais._vessels_lock:
+            v1 = ais._vessels.get(111111111)
+            v2 = ais._vessels.get(222222222)
+        assert v1 is not None
+        assert v1["source"] == "aishub"
+        assert v1["lat"] == 40.0
+        assert v1["name"] == "SHIP A"
+        assert v2 is not None
+        assert v2["source"] == "aishub"
+        assert v2["type"] == "passenger"  # AIS type 60 → passenger
+
+    def test_does_not_overwrite_fresh_live_data(self, monkeypatch):
+        """If the WebSocket pushed an update for an MMSI 0.5s ago and the
+        AISHub poll completes in that window, we should NOT clobber the
+        fresher live data."""
+        from services.fetchers import aishub_fallback
+        from services import ais_stream as ais
+
+        monkeypatch.setenv("AISHUB_USERNAME", "test-user")
+        self._force_primary_disconnected()
+
+        # Pre-seed _vessels with a "very fresh" live record.
+        fresh_ts = time.time()
+        with ais._vessels_lock:
+            ais._vessels[111111111] = {
+                "mmsi": 111111111,
+                "lat": 12.34,
+                "lng": 56.78,
+                "source": "aisstream",
+                "_updated": fresh_ts,
+            }
+
+        payload = json.dumps([
+            {"ERROR": False, "USERNAME": "test-user", "FORMAT": "1", "RECORDS": 1},
+            [
+                {
+                    "MMSI": 111111111,
+                    "LATITUDE": 99.0,  # bogus to make the test obvious
+                    "LONGITUDE": 99.0,
+                    "NAME": "STALE",
+                    "SOG": 0,
+                    "COG": 0,
+                    "TYPE": 0,
+                },
+            ],
+        ])
+
+        class FakeResp:
+            status_code = 200
+            text = payload
+
+        monkeypatch.setattr(
+            aishub_fallback, "fetch_with_curl", lambda *a, **kw: FakeResp()
+        )
+
+        # Note: 99.0/99.0 also exceeds the 91/181 sentinel guard and
+        # would be filtered. Pick a valid-but-bogus position instead.
+        payload = json.dumps([
+            {"ERROR": False, "USERNAME": "test-user", "FORMAT": "1", "RECORDS": 1},
+            [
+                {
+                    "MMSI": 111111111,
+                    "LATITUDE": 0.0,  # different from the live 12.34
+                    "LONGITUDE": 0.0,
+                    "NAME": "STALE",
+                    "SOG": 0,
+                    "COG": 0,
+                    "TYPE": 0,
+                },
+            ],
+        ])
+        monkeypatch.setattr(
+            aishub_fallback, "fetch_with_curl",
+            lambda *a, **kw: type("R", (), {"status_code": 200, "text": payload})(),
+        )
+
+        aishub_fallback.fetch_aishub_vessels()
+
+        with ais._vessels_lock:
+            v = ais._vessels.get(111111111)
+        # Live data wins — position should still be 12.34 / 56.78.
+        assert v["lat"] == 12.34
+        assert v["lng"] == 56.78
+        assert v["source"] == "aisstream"
+
+    def test_http_failure_returns_zero(self, monkeypatch):
+        from services.fetchers import aishub_fallback
+
+        monkeypatch.setenv("AISHUB_USERNAME", "test-user")
+        self._force_primary_disconnected()
+
+        class FailResp:
+            status_code = 503
+            text = ""
+
+        monkeypatch.setattr(
+            aishub_fallback, "fetch_with_curl", lambda *a, **kw: FailResp()
+        )
+
+        assert aishub_fallback.fetch_aishub_vessels() == 0