diff common/capstr.c common/capstr.c
--- common/capstr.c	Tue Jul 25 21:18:17 2000
+++ common/capstr.c	Wed Jul 26 20:25:46 2000
@@ -71,7 +71,8 @@
  */
 
 #define CAPABILITY "+1.11 diplomat_investigate_fix production_change_fix" \
-" game_ruleset nuclear_fallout land_channel_requirement"
+" game_ruleset nuclear_fallout land_channel_requirement" \
+" cont_unavailable_units"
 
 /* "+1.11" is protocol for 1.11.0 stable release.
 
@@ -91,6 +92,8 @@
    "land_channel_requirement" extends the protocol for the requirement
    of a minimum number of ocean tiles adjacent to a land tile wished to
    be changed to ocean.
+
+   "cont_unavailable_units" FIXME
 */
 
 void init_our_capability(void)
diff common/game.h common/game.h
--- common/game.h	Tue Jul 25 21:18:18 2000
+++ common/game.h	Wed Jul 26 20:25:48 2000
@@ -48,6 +48,8 @@
 #define CONTAMINATION_POLLUTION 1
 #define CONTAMINATION_FALLOUT   2
 
+#define CONT_UNIT_FOREVER -1
+
 struct civ_game {
   int is_new_game;		/* 1 for games never started */
   int version;
@@ -160,6 +162,7 @@
     int hut_overflight;
     int pillage_select;
     int nuke_contamination;
+    int cont_unavailable_units;
   } rgame;
 
   char demography[MAX_LEN_DEMOGRAPHY];
diff common/packets.c common/packets.c
--- common/packets.c	Wed Jul 26 19:40:00 2000
+++ common/packets.c	Wed Jul 26 20:25:47 2000
@@ -3427,6 +3427,9 @@
 if (pc && has_capability("nuclear_fallout", pc->capability)) {
   cptr=put_uint8(cptr, packet->nuke_contamination);
 }
+if (pc && has_capability("cont_unavailable_units", pc->capability)) {
+  cptr=put_sint16(cptr, packet->cont_unavailable_units);
+}
 
   put_uint16(buffer, cptr-buffer);
   return send_connection_data(pc, buffer, cptr-buffer);
@@ -3455,6 +3458,11 @@
   iget_uint8(&iter, &packet->nuke_contamination);
 } else {
   packet->nuke_contamination = CONTAMINATION_POLLUTION;
+}
+if (pc && has_capability("cont_unavailable_units", pc->capability)) {
+  iget_sint16(&iter, &packet->cont_unavailable_units);
+} else {
+  packet->cont_unavailable_units = CONT_UNIT_FOREVER;
 }
 
   pack_iter_end(&iter, pc);
diff common/packets.h common/packets.h
--- common/packets.h	Tue Jul 25 21:18:21 2000
+++ common/packets.h	Wed Jul 26 20:25:46 2000
@@ -726,6 +726,7 @@
   int hut_overflight;
   int pillage_select;
   int nuke_contamination;
+  int cont_unavailable_units;
 };
 
 /*********************************************************
diff data/civ1/game.ruleset data/civ1/game.ruleset
--- data/civ1/game.ruleset	Mon Jul 10 04:48:07 2000
+++ data/civ1/game.ruleset	Wed Jul 26 20:27:00 2000
@@ -38,3 +38,9 @@
 ;   "Pollution" - Pollution (same as industrial/population-generated).
 ;   "Fallout"   - Nuclear Fallout (distinct from industrial/population).
 nuke_contamination	= "Pollution"
+
+; Can city continue unit building if its conqueror does not have required tech.
+;   0           - Production must be changed immediately.
+;   1           - City can make one unit.
+;   "Forever"   - City can continue producing units forever.
+cont_unavailable_units  = "Forever"
diff data/civ2/game.ruleset data/civ2/game.ruleset
--- data/civ2/game.ruleset	Mon Jul 10 04:48:08 2000
+++ data/civ2/game.ruleset	Wed Jul 26 20:27:02 2000
@@ -38,3 +38,9 @@
 ;   "Pollution" - Pollution (same as industrial/population-generated).
 ;   "Fallout"   - Nuclear Fallout (distinct from industrial/population).
 nuke_contamination	= "Pollution"
+
+; Can city continue unit building if its conqueror does not have required tech.
+;   0           - Production must be changed immediately.
+;   1           - City can make one unit.
+;   "Forever"   - City can continue producing units forever.
+cont_unavailable_units  = "Forever"
diff data/default/game.ruleset data/default/game.ruleset
--- data/default/game.ruleset	Mon Jul 10 04:48:10 2000
+++ data/default/game.ruleset	Wed Jul 26 20:44:21 2000
@@ -38,3 +38,9 @@
 ;   "Pollution" - Pollution (same as industrial/population-generated).
 ;   "Fallout"   - Nuclear Fallout (distinct from industrial/population).
 nuke_contamination	= "Fallout"
+
+; Can city continue unit building if its conqueror does not have required tech.
+;   0           - Production must be changed immediately.
+;   1           - City can make one unit.
+;   "Forever"   - City can continue producing units forever.
+cont_unavailable_units  = "Forever"
diff server/cityturn.c server/cityturn.c
--- server/cityturn.c	Tue Jul 25 21:18:35 2000
+++ server/cityturn.c	Wed Jul 26 20:25:45 2000
@@ -77,6 +77,7 @@
 static void upgrade_building_prod(struct city *pcity);
 static Unit_Type_id unit_upgrades_to(struct city *pcity, Unit_Type_id id);
 static void upgrade_unit_prod(struct city *pcity);
+static void change_production_from_unavailable(struct city *pcity);
 static void obsolete_building_test(struct city *pcity, int b1, int b2);
 static void pay_for_buildings(struct player *pplayer, struct city *pcity);
 
@@ -1340,6 +1341,13 @@
 
     upgrade_unit_prod(pcity);
 
+    if(get_invention(pplayer,
+                     unit_types[pcity->currently_building].tech_requirement)
+         != TECH_KNOWN && game.rgame.cont_unavailable_units == 0)
+    {
+      change_production_from_unavailable(pcity);
+    }
+
     /* FIXME: F_CITIES should be changed to any unit
      * that 'contains' 1 (or more) pop -- sjolie
      */
@@ -1385,9 +1393,16 @@
 	 If there's nothing there, worklist_change_build_target won't
 	 do anything. */
       worklist_change_build_target(pplayer, pcity);
+      if (pcity->is_building_unit &&
+          get_invention(pplayer,
+            unit_types[pcity->currently_building].tech_requirement)!=
+          TECH_KNOWN && game.rgame.cont_unavailable_units != CONT_UNIT_FOREVER)
+      {
+        change_production_from_unavailable(pcity);
+      }
 
 
-    gamelog(GAMELOG_UNIT, "%s build %s in %s (%i,%i)",
+   gamelog(GAMELOG_UNIT, "%s build %s in %s (%i,%i)",
 	    get_nation_name_plural(pplayer->nation), 
 	    unit_types[pcity->currently_building].name,
 	    pcity->name, pcity->x, pcity->y);
@@ -1396,6 +1411,23 @@
     }
   }
 return 1;
+}
+
+/**************************************************************************
+...
+**************************************************************************/
+static void change_production_from_unavailable(struct city *pcity)
+{
+   Unit_Type_id old_prod;
+
+   old_prod = pcity->currently_building;
+   pcity->currently_building=best_role_unit(pcity, L_FIRSTBUILD);
+   notify_player_ex(&game.players[pcity->owner], pcity->x, pcity->y,
+                    E_UNIT_UPGRADED, 
+                    _("Game: %s cant build %s. It is building %s instead."),
+                    pcity->name,
+                    get_unit_type(old_prod)->name,
+                    get_unit_type(pcity->currently_building)->name);
 }
 
 /**************************************************************************
diff server/ruleset.c server/ruleset.c
--- server/ruleset.c	Thu Jul 13 17:45:40 2000
+++ server/ruleset.c	Wed Jul 26 20:32:43 2000
@@ -1943,6 +1943,18 @@
     game.rgame.nuke_contamination = CONTAMINATION_POLLUTION;
   }
 
+  sval = secfile_lookup_str_int(&file, &game.rgame.cont_unavailable_units,
+                                "civstyle.cont_unavailable_units" );
+  if (sval != 0) {
+    if (mystrcasecmp(sval, "Forever") == 0) {
+      game.rgame.cont_unavailable_units = CONT_UNIT_FOREVER;
+    } else {
+      freelog(LOG_NORMAL, _("Bad value %s for cont_unavailable_units. Using "
+              "\"Forever\"."), sval);
+      game.rgame.cont_unavailable_units = CONT_UNIT_FOREVER;
+    }
+  }
+
   section_file_check_unused(&file, filename);
   section_file_free(&file);
 }
@@ -2293,6 +2305,7 @@
   misc_p.hut_overflight = game.rgame.hut_overflight;
   misc_p.pillage_select = game.rgame.pillage_select;
   misc_p.nuke_contamination = game.rgame.nuke_contamination;
+  misc_p.cont_unavailable_units = game.rgame.cont_unavailable_units;
 
   for(to = 0; to < game.nplayers; to++) {           /* dests */
     if(dest==0 || get_player(to)==dest) {