diff -u3NrX /home/perrin/freeciv/diff_ignore freeciv/ai/advmilitary.c freeciv-phased/ai/advmilitary.c
--- freeciv/ai/advmilitary.c	Thu Mar  7 13:17:24 2002
+++ freeciv-phased/ai/advmilitary.c	Tue Mar 12 17:13:27 2002
@@ -164,7 +164,8 @@
   int v;
   bool sailing;
 
-  if (unit_flag(punit, F_NO_LAND_ATTACK)) return(0);
+  if (unit_flag(punit, F_NO_LAND_ATTACK) 
+      && city_got_building(pcity, B_COASTAL)) return(0); /* harmless */
   sailing = is_sailing_unit(punit);
   if (sailing && !is_terrain_near_tile(pcity->x, pcity->y, T_OCEAN)) return(0);
 
@@ -477,6 +478,9 @@
   memset(desire, 0, sizeof(desire));
   unit_type_iterate(i) {
     if (!is_ai_simple_military(i)) continue;
+    if (unit_type_flag(i, F_PARTIAL_INVIS) && ai_handicap(pplayer, H_SUB)) {
+      return;
+    }
     m = unit_types[i].move_type;
     if ((m == LAND_MOVING || m == SEA_MOVING)) {
       k = num_unknown_techs_for_goal(pplayer,unit_types[i].tech_requirement);
diff -u3NrX /home/perrin/freeciv/diff_ignore freeciv/ai/aiunit.c freeciv-phased/ai/aiunit.c
--- freeciv/ai/aiunit.c	Thu Mar  7 13:17:25 2002
+++ freeciv-phased/ai/aiunit.c	Tue Mar 12 17:09:51 2002
@@ -2290,7 +2290,6 @@
 {
   return !unit_type_flag(type, F_NONMIL)
     && !unit_type_flag(type, F_MISSILE)
-    && !unit_type_flag(type, F_NO_LAND_ATTACK)
     && !(get_unit_type(type)->transport_capacity >= 8);
 }
 
diff -u3NrX /home/perrin/freeciv/diff_ignore freeciv/common/combat.c freeciv-phased/common/combat.c
--- freeciv/common/combat.c	Mon Mar 11 20:36:37 2002
+++ freeciv-phased/common/combat.c	Tue Mar 12 16:57:30 2002
@@ -446,8 +446,9 @@
 have anything to do with the value of a unit.
 It would be nice if the function was a bit more fuzzy about prioritizing,
 making it able to fx choose a 1a/9d unit over a 10a/10d unit. It should
-also be able to spare units without full hp's to some extend, as these
+also be able to spare units without full hp's to some extent, as these
 could be more valuable later.
+A seaborne unit must attempt to defend a city against submarine attacks.
 **************************************************************************/
 struct unit *get_defender(struct unit *attacker, int x, int y)
 {
@@ -466,6 +467,11 @@
 
       /* This will make units roughly evenly good defenders look alike. */
       int unit_def = (int) (100000 * (1 - unit_win_chance(attacker, defender)));
+      /* F_NO_LAND_ATTACK units can only attack seaborne units, so let us
+         give them something to chew on. Go, subs, go! {:-) - Per */
+      if (unit_flag(attacker, F_NO_LAND_ATTACK)
+          && is_sailing_unit(defender))
+              unit_def += 100001;
       assert(unit_def >= 0);
 
       if (unit_def > bestvalue) {
diff -u3NrX /home/perrin/freeciv/diff_ignore freeciv/common/player.h freeciv-phased/common/player.h
--- freeciv/common/player.h	Thu Mar  7 13:17:30 2002
+++ freeciv-phased/common/player.h	Tue Mar 12 17:12:54 2002
@@ -47,7 +47,7 @@
   H_CITYUNITS=16, /* doesn't know what units are in enemy cities */
   H_STACKS=32, /* doesn't know what units are in stacks */
   H_VETERAN=64, /* doesn't know veteran status of enemy units */
-  H_SUB=128, /* doesn't know where subs may be lurking */
+  H_SUB=128, /* doesn't know how to use subs or other partially invisible units */
 /* below this point are milder handicaps that I can actually implement -- Syela */
   H_RATES=256, /* can't set its rates beyond government limits */
   H_TARGETS=512, /* can't target anything it doesn't know exists */
diff -u3NrX /home/perrin/freeciv/diff_ignore freeciv/server/stdinhand.c freeciv-phased/server/stdinhand.c
--- freeciv/server/stdinhand.c	Mon Mar 11 20:36:40 2002
+++ freeciv-phased/server/stdinhand.c	Tue Mar 12 17:07:53 2002
@@ -1646,9 +1646,9 @@
   int h[11] = { -1, 
 		H_NONE, 
 		H_NONE, 
-		H_RATES | H_TARGETS | H_HUTS,
+		H_RATES | H_TARGETS | H_HUTS | H_SUB,
 		H_NONE, 
-		H_RATES | H_TARGETS | H_HUTS, 
+		H_RATES | H_TARGETS | H_HUTS | H_SUB, 
 		H_NONE, 
 		H_NONE, 
 		H_NONE, 
diff -u3NrX /home/perrin/freeciv/diff_ignore freeciv/server/unittools.c freeciv-phased/server/unittools.c
--- freeciv/server/unittools.c	Thu Mar  7 13:17:36 2002
+++ freeciv-phased/server/unittools.c	Tue Mar 12 17:30:15 2002
@@ -139,7 +139,17 @@
     return FALSE;
   }
 
-  if (unit_flag(punit, F_NO_LAND_ATTACK) && totile!=T_OCEAN)  {
+  /* no_land_attack units can only attack seaborne units, and cannot
+     attack coastal fortresses  */
+  if ((unit_flag(punit, F_NO_LAND_ATTACK))
+      && (!is_sailing_unit(pdefender))) {
+    notify_player(unit_owner(punit), "Game: Target has no seaborne units");
+    return FALSE;
+  }
+  if ((unit_flag(punit, F_NO_LAND_ATTACK))
+      && (map_get_city(dest_x,dest_y)
+        && city_got_building(map_get_city(dest_x, dest_y), B_COASTAL))) {
+    notify_player(unit_owner(punit), "Game: City is protected by a costal fortress");
     return FALSE;
   }