diff --git a/backend/services/deployment_history.py b/backend/services/deployment_history.py
index d9002fc..0186eb8 100644
--- a/backend/services/deployment_history.py
+++ b/backend/services/deployment_history.py
@@ -229,6 +229,48 @@ def get_deployment_history_data(
 
     projects_data.sort(key=lambda p: (p["first_active"] or "9999", p["name"]))
 
+    # ── Per-unit view data (Gantt-by-Unit tab) ────────────────────────
+    # Same source assignments, re-grouped by unit_id.  Each bar carries
+    # the project's color + name so the renderer can paint by job
+    # without doing a second lookup.
+    unit_bars: dict[str, list[dict]] = {}
+    project_lookup = {p["id"]: p for p in projects_data}
+    for a in assignments:
+        start = max(a.assigned_at.date() if a.assigned_at else first_date, first_date)
+        end_dt = a.assigned_until or now
+        end   = min(end_dt.date(), last_date)
+        if end < start:
+            continue
+        p_info = project_lookup.get(a.project_id, {})
+        unit_bars.setdefault(a.unit_id, []).append({
+            "project_id":    a.project_id,
+            "project_name":  p_info.get("name", "(deleted project)"),
+            "project_color": p_info.get("color", _color_for_project(a.project_id)),
+            "location_id":   a.location_id,
+            "location_name": loc_name_map.get(a.location_id, "(unknown location)"),
+            "start":         start.isoformat(),
+            "end":           end.isoformat(),
+            "is_active":     a.assigned_until is None,
+            "source":        a.source,
+        })
+
+    # Sort units by first-active date so the most-recently-deployed
+    # units sit at the top.  Reverse if we want oldest-first.
+    units_data = []
+    for uid, bars in unit_bars.items():
+        bars.sort(key=lambda b: b["start"])
+        first_start = bars[0]["start"]
+        # "active now" flag = any bar is still active
+        any_active = any(b["is_active"] for b in bars)
+        units_data.append({
+            "id":              uid,
+            "bars":            bars,
+            "first_active":    first_start,
+            "assignment_count": len(bars),
+            "any_active":      any_active,
+        })
+    units_data.sort(key=lambda u: (not u["any_active"], u["first_active"], u["id"]))
+
     # Now build the months array.
     months_data = []
     cur_year, cur_month = start_year, start_month
@@ -267,6 +309,7 @@ def get_deployment_history_data(
     return {
         "months":   months_data,
         "projects": projects_data,
+        "units":    units_data,
         "total_assignments":    len(assignments),
         "total_active_units":   len(distinct_units),
         "window": {
diff --git a/templates/admin/deployment_history.html b/templates/admin/deployment_history.html
index e77d0b0..e80b6a8 100644
--- a/templates/admin/deployment_history.html
+++ b/templates/admin/deployment_history.html
@@ -97,7 +97,7 @@
     </div>
 </div>
 
-<!-- View tabs: Calendar | Gantt -->
+<!-- View tabs: Calendar | Gantt (by project) | By Unit (gantt by unit) -->
 <div class="flex rounded-lg bg-gray-100 dark:bg-gray-700 p-1 mb-6 w-fit">
     <button id="dh-tab-calendar" onclick="switchDhView('calendar')"
             class="px-4 py-2 rounded-md text-sm font-medium transition-colors bg-white dark:bg-slate-600 text-gray-900 dark:text-white shadow">
@@ -105,7 +105,11 @@
     </button>
     <button id="dh-tab-gantt" onclick="switchDhView('gantt')"
             class="px-4 py-2 rounded-md text-sm font-medium transition-colors text-gray-600 dark:text-gray-300 hover:text-gray-900 dark:hover:text-white">
-        Gantt
+        Gantt by Project
+    </button>
+    <button id="dh-tab-byunit" onclick="switchDhView('byunit')"
+            class="px-4 py-2 rounded-md text-sm font-medium transition-colors text-gray-600 dark:text-gray-300 hover:text-gray-900 dark:hover:text-white">
+        Gantt by Unit
     </button>
 </div>
 
@@ -272,6 +276,50 @@
 {% endif %}
 </div>  {# /#dh-view-gantt #}
 
+<!-- ─── Gantt-by-Unit view ─── -->
+<div id="dh-view-byunit" class="hidden">
+{% if calendar.units %}
+    <div class="bg-white dark:bg-slate-800 rounded-xl shadow-lg p-4 mb-6 overflow-x-auto">
+        <p class="text-xs text-gray-500 dark:text-gray-400 mb-3">
+            One row per seismograph that had ≥1 assignment in this window.
+            Bars are colored by <strong>project</strong>, so an operator can read where each unit travelled
+            across jobs.  Active deployments end at "now" with a small white tip.
+            Click a unit ID to open its detail page; click a bar to open the bar's project.
+        </p>
+        <svg id="dh-byunit-svg" preserveAspectRatio="none"
+             style="width: 100%; min-width: 800px;"></svg>
+    </div>
+
+    <div class="flex items-center justify-center gap-3 mb-8">
+        <a href="/tools/deployment-history?year={{ prev_year }}&month={{ prev_month }}#byunit"
+           class="px-3 py-2 rounded-lg bg-gray-100 dark:bg-gray-700 hover:bg-gray-200 dark:hover:bg-gray-600 text-gray-700 dark:text-gray-300"
+           title="Previous month">
+            <svg class="w-5 h-5" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+                <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M15 19l-7-7 7-7"/>
+            </svg>
+        </a>
+        <span class="text-lg font-bold text-gray-900 dark:text-white px-3">
+            {{ calendar.months[0].short_name }} '{{ calendar.months[0].year_short }} – {{ calendar.months[11].short_name }} '{{ calendar.months[11].year_short }}
+        </span>
+        <a href="/tools/deployment-history?year={{ next_year }}&month={{ next_month }}#byunit"
+           class="px-3 py-2 rounded-lg bg-gray-100 dark:bg-gray-700 hover:bg-gray-200 dark:hover:bg-gray-600 text-gray-700 dark:text-gray-300"
+           title="Next month">
+            <svg class="w-5 h-5" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+                <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M9 5l7 7-7 7"/>
+            </svg>
+        </a>
+        <a href="/tools/deployment-history#byunit"
+           class="ml-2 px-4 py-2 rounded-lg bg-seismo-orange text-white hover:bg-orange-600">
+            Recent
+        </a>
+    </div>
+{% else %}
+    <div class="bg-white dark:bg-slate-800 rounded-xl shadow-lg p-8 text-center text-gray-500 dark:text-gray-400">
+        <p class="text-sm">No unit deployments in this window.</p>
+    </div>
+{% endif %}
+</div>  {# /#dh-view-byunit #}
+
 <!-- Day-detail side panel -->
 <div id="dh-day-panel-backdrop"
      class="fixed inset-0 bg-black/30 z-40 hidden transition-opacity"
@@ -405,36 +453,41 @@ document.addEventListener('keydown', (e) => {
 });
 
 // ── Tab switcher ────────────────────────────────────────────────────
+const _DH_TABS = {
+    calendar: { view: 'dh-view-calendar', btn: 'dh-tab-calendar', hash: '',         render: null },
+    gantt:    { view: 'dh-view-gantt',    btn: 'dh-tab-gantt',    hash: '#gantt',   render: () => renderDhGantt() },
+    byunit:   { view: 'dh-view-byunit',   btn: 'dh-tab-byunit',   hash: '#byunit',  render: () => renderDhByUnit() },
+};
+
 function switchDhView(which) {
-    const cal   = document.getElementById('dh-view-calendar');
-    const gantt = document.getElementById('dh-view-gantt');
-    const btnC  = document.getElementById('dh-tab-calendar');
-    const btnG  = document.getElementById('dh-tab-gantt');
+    const target = _DH_TABS[which] || _DH_TABS.calendar;
     const activeCls = ['bg-white', 'dark:bg-slate-600', 'text-gray-900', 'dark:text-white', 'shadow'];
     const dormantCls = ['text-gray-600', 'dark:text-gray-300', 'hover:text-gray-900', 'dark:hover:text-white'];
-    if (which === 'gantt') {
-        cal.classList.add('hidden');
-        gantt.classList.remove('hidden');
-        btnG.classList.add(...activeCls);   btnG.classList.remove(...dormantCls);
-        btnC.classList.remove(...activeCls); btnC.classList.add(...dormantCls);
-        if (window.location.hash !== '#gantt') {
-            history.replaceState(null, '', window.location.pathname + window.location.search + '#gantt');
-        }
-        renderDhGantt();
-    } else {
-        gantt.classList.add('hidden');
-        cal.classList.remove('hidden');
-        btnC.classList.add(...activeCls);    btnC.classList.remove(...dormantCls);
-        btnG.classList.remove(...activeCls); btnG.classList.add(...dormantCls);
-        if (window.location.hash === '#gantt') {
-            history.replaceState(null, '', window.location.pathname + window.location.search);
-        }
+    // Hide all views, dormant-style all tabs, then activate the chosen one.
+    for (const key of Object.keys(_DH_TABS)) {
+        const t = _DH_TABS[key];
+        const v = document.getElementById(t.view);
+        const b = document.getElementById(t.btn);
+        if (v) v.classList.add('hidden');
+        if (b) { b.classList.remove(...activeCls); b.classList.add(...dormantCls); }
     }
+    const v = document.getElementById(target.view);
+    const b = document.getElementById(target.btn);
+    if (v) v.classList.remove('hidden');
+    if (b) { b.classList.add(...activeCls); b.classList.remove(...dormantCls); }
+    // URL hash sync.
+    const wanted = target.hash;
+    const cur    = window.location.hash || '';
+    if (cur !== wanted) {
+        history.replaceState(null, '', window.location.pathname + window.location.search + wanted);
+    }
+    if (target.render) target.render();
 }
 
-// Land on the Gantt view if URL hash is #gantt.
-if (window.location.hash === '#gantt') {
-    document.addEventListener('DOMContentLoaded', () => switchDhView('gantt'));
+// Land on the requested view if the URL hash matches.
+const _initialHash = window.location.hash;
+if (_initialHash === '#gantt' || _initialHash === '#byunit') {
+    document.addEventListener('DOMContentLoaded', () => switchDhView(_initialHash.slice(1)));
 }
 
 // ── Gantt renderer ──────────────────────────────────────────────────
@@ -546,5 +599,113 @@ function renderDhGantt() {
     svg.setAttribute('height', height);
     svg.innerHTML = monthsParts.join('') + rowParts.join('') + todayMarker;
 }
+
+// ── Gantt-by-Unit renderer ──────────────────────────────────────────
+// Inverts the Gantt: rows = seismographs, bars = assignment windows
+// colored by project (so an operator can read where each unit went
+// across jobs).  Shares the time-axis geometry with renderDhGantt().
+const _dhUnits = {{ calendar.units | tojson }};
+let _byunitRendered = false;
+function renderDhByUnit() {
+    if (_byunitRendered) return;
+    _byunitRendered = true;
+    const svg = document.getElementById('dh-byunit-svg');
+    if (!svg) return;
+    if (!_dhUnits || _dhUnits.length === 0) {
+        svg.innerHTML = '';
+        return;
+    }
+
+    const isDark = document.documentElement.classList.contains('dark');
+    const labelColor = isDark ? '#9ca3af' : '#6b7280';
+    const labelStrong = isDark ? '#e5e7eb' : '#111827';
+    const gridColor  = isDark ? '#374151' : '#e5e7eb';
+    const rowAltBg   = isDark ? '#1e293b' : '#f9fafb';
+    const todayColor = '#f48b1c';
+
+    const containerW = svg.parentElement.clientWidth || 1000;
+    const width      = Math.max(containerW, 800);
+    const labelW     = 160;
+    const padTop     = 36;
+    const padBottom  = 16;
+    const rowH       = 32;
+    const barH       = 16;
+    const height     = padTop + padBottom + _dhUnits.length * rowH;
+
+    const usableW = width - labelW - 8;
+    const tStart = new Date(_dhWindowStart + 'T00:00:00Z').getTime();
+    const tEnd   = new Date(_dhWindowEnd   + 'T23:59:59Z').getTime();
+    const tRange = tEnd - tStart;
+    const xFor = (d) => {
+        const ms = (typeof d === 'string') ? new Date(d + 'T00:00:00Z').getTime() : d;
+        return labelW + Math.max(0, Math.min(usableW, (ms - tStart) / tRange * usableW));
+    };
+
+    // Month gridlines + labels (same as renderDhGantt).
+    const monthsParts = [];
+    const cursor = new Date(_dhWindowStart + 'T00:00:00Z');
+    cursor.setUTCDate(1);
+    while (cursor.getTime() <= tEnd) {
+        const x = xFor(cursor);
+        const label = cursor.toLocaleDateString('en-US', { month: 'short', year: '2-digit', timeZone: 'UTC' });
+        monthsParts.push(`<line x1="${x}" y1="${padTop}" x2="${x}" y2="${height - padBottom}" stroke="${gridColor}" stroke-width="1"/>`);
+        monthsParts.push(`<text x="${x + 2}" y="${padTop - 6}" font-size="10" fill="${labelColor}" font-family="system-ui,sans-serif">${label}</text>`);
+        cursor.setUTCMonth(cursor.getUTCMonth() + 1);
+    }
+
+    const now = Date.now();
+    let todayMarker = '';
+    if (now >= tStart && now <= tEnd) {
+        const x = xFor(now);
+        todayMarker = `<line x1="${x}" y1="${padTop}" x2="${x}" y2="${height - padBottom}" stroke="${todayColor}" stroke-width="2" stroke-dasharray="3 2" opacity="0.85"/>
+            <text x="${x + 3}" y="${padTop - 20}" font-size="9" fill="${todayColor}" font-family="system-ui,sans-serif">today</text>`;
+    }
+
+    const rowParts = [];
+    _dhUnits.forEach((unit, idx) => {
+        const y = padTop + idx * rowH;
+        if (idx % 2 === 1) {
+            rowParts.push(`<rect x="0" y="${y}" width="${width}" height="${rowH}" fill="${rowAltBg}"/>`);
+        }
+        // Unit label: opens /unit/{id} when clicked.  Active-now dot.
+        const activeDot = unit.any_active
+            ? `<circle cx="12" cy="${y + rowH / 2}" r="3.5" fill="#22c55e"/>`
+            : `<circle cx="12" cy="${y + rowH / 2}" r="3.5" fill="${labelColor}" opacity="0.4"/>`;
+        rowParts.push(`<a href="/unit/${_dhEsc(unit.id)}" target="_top">
+            <rect x="0" y="${y}" width="${labelW}" height="${rowH}" fill="transparent"/>
+            ${activeDot}
+            <text x="22" y="${y + rowH / 2 + 4}" font-size="12" fill="${labelStrong}"
+                  font-family="system-ui,sans-serif" font-weight="500">
+                ${_dhEsc(unit.id)}
+            </text>
+            <text x="${labelW - 8}" y="${y + rowH / 2 + 4}" font-size="10" fill="${labelColor}"
+                  text-anchor="end" font-family="system-ui,sans-serif">
+                ${unit.assignment_count}
+            </text>
+        </a>`);
+        // Bars — colored by the bar's project (not the row).
+        for (const bar of (unit.bars || [])) {
+            const x1 = xFor(bar.start);
+            const x2 = xFor(bar.end);
+            const barW = Math.max(x2 - x1, 2);
+            const by = y + (rowH - barH) / 2;
+            const tip = `${bar.project_name}\n${bar.location_name}\n${bar.start} → ${bar.is_active ? 'present' : bar.end}`;
+            rowParts.push(`<a href="/projects/${_dhEsc(bar.project_id)}" target="_top">
+                <g style="cursor: pointer;">
+                    <title>${_dhEsc(tip)}</title>
+                    <rect x="${x1}" y="${by}" width="${barW}" height="${barH}"
+                          rx="3"
+                          fill="${bar.project_color}" opacity="${bar.is_active ? 1.0 : 0.75}"
+                          ${bar.source === 'metadata_backfill' ? 'stroke="#3b82f6" stroke-width="1.5"' : ''}/>
+                    ${bar.is_active ? `<rect x="${x2 - 3}" y="${by}" width="3" height="${barH}" fill="#ffffff" opacity="0.8"/>` : ''}
+                </g>
+            </a>`);
+        }
+    });
+
+    svg.setAttribute('viewBox', `0 0 ${width} ${height}`);
+    svg.setAttribute('height', height);
+    svg.innerHTML = monthsParts.join('') + rowParts.join('') + todayMarker;
+}
 </script>
 {% endblock %}