diff --git a/plan/forces.md b/plan/forces.md
index a1b14f5..d0d6820 100644
--- a/plan/forces.md
+++ b/plan/forces.md
@@ -118,6 +118,17 @@ editor — porting MegaMekLab is [declined](declined.md), and
       model as two fields and a display name that folds a Clan design's second
       name in; the lookup has to match all three, because a player types
       `nova prime` and means `Black Hawk (Nova) Prime`.
+- [ ] **Make `era` mean an era.** The Hangar's query language leaves the key
+      unclaimed on purpose. A year is when a design was introduced and the
+      index carries it; an era is a period a design was available in, and a
+      2750 machine belongs to the Star League and to the Dark Age both.
+      Both halves of the answer are in the release already: the periods and
+      their bounds are `data/universe/eras.xml`, fourteen of them from
+      Pre-Spaceflight to ilClan, and availability is
+      `megamek.common.TechAdvancement`, which holds introduction, extinction
+      and reintroduction dates rather than one year. Neither is in the index,
+      so the key is listed as coming soon rather than quietly answered with
+      `year`, and the force target's field is a Year.
 - [ ] **Filter with the same predicate the server uses**, compiled to wasm —
       [unit-search](unit-search.md)'s open decision, and this screen is the
       consumer that makes it due.
diff --git a/web/scripts/hangar.test.mjs b/web/scripts/hangar.test.mjs
index a665879..8c26e70 100644
--- a/web/scripts/hangar.test.mjs
+++ b/web/scripts/hangar.test.mjs
@@ -424,6 +424,7 @@ test("the filter reference says what is not supported yet, and marks it", async
   // does not carry.
   const hangar = await readFile(`${web}src/screens/hangar.ts`, "utf8");
   for (const missing of [
+    "era",
     "equipment",
     "quirks",
     "damage",
@@ -432,7 +433,7 @@ test("the filter reference says what is not supported yet, and marks it", async
   ]) {
     assert.match(
       hangar,
-      new RegExp(`soon\\("${missing}"`),
+      new RegExp(`soon\\(\\s*"${missing}"`),
       `${missing} is not listed as unsupported`,
     );
   }
@@ -445,6 +446,34 @@ test("the filter reference says what is not supported yet, and marks it", async
   assert.equal(parseQuery('equipment:"ER PPC"').filters.length, 0);
 });
 
+test("era is not another word for year, and is not accepted", () => {
+  // A year is when a design was introduced; an era is a period it was
+  // available in, and a 2750 design belongs to Star League and to Dark Age
+  // both. Taking `era` as `year` would answer a different question quietly.
+  assert.equal(parseQuery("era:jihad").filters.length, 0);
+  assert.equal(parseQuery("era<=3025").filters.length, 0);
+  assert.ok(!FILTER_KEYS.includes("era"), "era is still claimed as a key");
+  assert.deepEqual(parseQuery("year<=3025").filters, [
+    { key: "year", op: "<=", value: "3025" },
+  ]);
+});
+
+test("weight asks the same question as mass", () => {
+  const light = { name: "Locust LCT-1V", chassis: "Locust", mass: 20 };
+  const heavy = { name: "Atlas AS7-D", chassis: "Atlas", mass: 100 };
+  assert.deepEqual(
+    search([light, heavy], "weight>=70").map((u) => u.chassis),
+    ["Atlas"],
+  );
+  for (const key of ["mass", "tons", "tonnage", "weight"]) {
+    assert.equal(
+      search([light, heavy], `${key}<=20`).length,
+      1,
+      `${key} does not read tonnage`,
+    );
+  }
+});
+
 test("the reference explains every key the box accepts", async () => {
   // The list under Filters is the only place a key's meaning is written down,
   // so a key the parser takes and the dialog omits is a key nobody can learn.
diff --git a/web/src/screens/hangar.ts b/web/src/screens/hangar.ts
index d4fa2af..b37af05 100644
--- a/web/src/screens/hangar.ts
+++ b/web/src/screens/hangar.ts
@@ -199,20 +199,17 @@ export function hangarScreen(): Node[] {
           "Bare words match a design's name. A term filters one column: a key, then one of : = < <= > >=, then a value. Terms combine with and.",
       }),
       el("ul", { className: "hangar-help-examples" }, [
-        example(
-          "atlas",
-          "39 designs: the Atlas, the Atlas II and the Atlas III",
-        ),
+        example("atlas", "39 designs: every Atlas, Atlas II and Atlas III"),
         example(
           "hawk",
-          "193, because a bare word reads the model as well as the chassis",
+          "193: a Phoenix Hawk, a Black Hawk and a Battle Hawk all answer to it",
         ),
         example(
           'chassis:"black hawk"',
-          "33: the Black Hawks alone, quoted because the name has a space in it",
+          "33: the Black Hawks, and no Phoenix Hawk. Quoted, because the name has a space in it",
         ),
         example(
-          "class:heavy jump>0 era<=3025",
+          "class:heavy jump>0 year<=3025",
           "heavies that jump, introduced by 3025",
         ),
       ]),
@@ -247,8 +244,8 @@ export function hangarScreen(): Node[] {
         ),
         filter("bv", "battle value.", "bv<=1500"),
         filter("cost", "the price in C-bills.", "cost<5000000"),
-        filter("mass, tons, tonnage", "tonnage.", "mass>=70"),
-        filter("era, year", "the year the design was introduced.", "era<=3025"),
+        filter("mass, tons, tonnage, weight", "tonnage.", "mass>=70"),
+        filter("year", "the year the design was introduced.", "year<=3025"),
         filter(
           "armor, armour",
           "armour points over the whole machine.",
@@ -274,6 +271,11 @@ export function hangarScreen(): Node[] {
       ]),
       el("h3", { textContent: "Not yet" }),
       el("ul", { className: "hangar-help-soon" }, [
+        soon(
+          "era",
+          "era:jihad",
+          "whether a design was available in a named era, which a year of introduction cannot answer",
+        ),
         soon("equipment", 'equipment:"ER PPC"', "what a design carries"),
         soon("quirks", "quirks:battlefists", "MegaMek's per-design quirks"),
         soon("damage", "damage9>=20", "damage at a range band"),
diff --git a/web/src/units.ts b/web/src/units.ts
index 767202c..495b5d8 100644
--- a/web/src/units.ts
+++ b/web/src/units.ts
@@ -212,17 +212,23 @@ export interface Query {
  * The columns a filter can name, and what each one is called in a query.
  *
  * Aliased where the word a player reaches for is not the column's name:
- * `era` and `year` are the same question, and so are `mass`, `tons` and
- * `tonnage`.
+ * `mass`, `tons`, `tonnage` and `weight` are one question, and so are `armor`
+ * and `armour`.
+ *
+ * `era` is deliberately absent. It is not another word for `year`: a year is
+ * when a design was introduced, an era is a period it was available in, and
+ * a design introduced in 2750 is a Star League machine and a Dark Age one
+ * both. Answering that needs the introduction, extinction and reintroduction
+ * dates the index does not carry, so the key is unclaimed rather than wrong.
  */
 const FIELDS: Record<string, { column: keyof Unit; kind: "number" | "text" }> =
   {
     year: { column: "year", kind: "number" },
-    era: { column: "year", kind: "number" },
     bv: { column: "bv", kind: "number" },
     mass: { column: "mass", kind: "number" },
     tons: { column: "mass", kind: "number" },
     tonnage: { column: "mass", kind: "number" },
+    weight: { column: "mass", kind: "number" },
     walk: { column: "walk_mp", kind: "number" },
     jump: { column: "jump_mp", kind: "number" },
     armor: { column: "total_armor", kind: "number" },