commit 284359aa27739ed350312a74d92bf51d2a071540
Author: Jacob Nevins <0jacobnk.fcdev@chiark.greenend.org.uk>
Date:   Sat Aug 26 14:54:14 2017 +0100

    Add Icebreaker units.

diff --git a/xpt/terrain.ruleset b/xpt/terrain.ruleset
index 26a74e4..e1afa0b 100644
--- a/xpt/terrain.ruleset
+++ b/xpt/terrain.ruleset
@@ -313,7 +313,7 @@ warmer_wetter_result = "no"
 warmer_drier_result  = "no"
 cooler_wetter_result = "Frozen Lake"
 cooler_drier_result  = "Frozen Lake"
-native_to            = "Sea", "Air", "Missile", "Helicopter", "Trireme"
+native_to            = "Sea", "Icebreaker", "Air", "Missile", "Helicopter", "Trireme"
 flags                = "NoCities", "NoBarbs", "NoPollution", "FreshWater", "NoZoc", "NoFortify"
 property_ocean_depth = 0
 color.r              = 46
@@ -356,7 +356,7 @@ warmer_wetter_result = "no"
 warmer_drier_result  = "no"
 cooler_wetter_result = "Sea Ice"
 cooler_drier_result  = "Sea Ice"
-native_to            = "Sea", "Air", "Missile", "Helicopter", "Trireme"
+native_to            = "Sea", "Icebreaker", "Air", "Missile", "Helicopter", "Trireme"
 flags                = "NoCities", "NoPollution", "UnsafeCoast", "NoZoc", "NoFortify"
 property_ocean_depth = 32
 color.r              = 0
@@ -400,7 +400,7 @@ warmer_wetter_result = "no"
 warmer_drier_result  = "no"
 cooler_wetter_result = "Deep Sea Ice"
 cooler_drier_result  = "Deep Sea Ice"
-native_to            = "Sea", "Air", "Missile", "Helicopter"
+native_to            = "Sea", "Icebreaker", "Air", "Missile", "Helicopter"
 flags                = "NoCities", "NoPollution", "UnsafeCoast", "NoZoc", "NoFortify"
 property_ocean_depth = 87
 color.r              = 0
@@ -1034,7 +1034,7 @@ graphic              = "lake_ice"
 graphic_alt          = "arctic"
 identifier           = "T"
 class                = "Oceanic"
-movement_cost        = 1
+movement_cost        = 2
 defense_bonus        = 0
 food                 = 0
 shield               = 0
@@ -1061,7 +1061,7 @@ warmer_wetter_result = "Lake"
 warmer_drier_result  = "Lake"
 cooler_wetter_result = "no"
 cooler_drier_result  = "no"
-native_to            = "Air", "Missile", "Helicopter"
+native_to            = "Air", "Missile", "Helicopter", "Icebreaker"
 flags                = "NoCities", "NoBarbs", "NoPollution", "UnsafeCoast", "FreshWater", "NoZoc", "NoFortify", "Frozen"
 property_ocean_depth = 0
 color.r              = 212
@@ -1078,7 +1078,7 @@ graphic              = "coast_ice"
 graphic_alt          = "arctic"
 identifier           = "U"
 class                = "Oceanic"
-movement_cost        = 1
+movement_cost        = 2
 defense_bonus        = 0
 food                 = 0
 shield               = 0
@@ -1105,7 +1105,7 @@ warmer_wetter_result = "Ocean"
 warmer_drier_result  = "Ocean"
 cooler_wetter_result = "no"
 cooler_drier_result  = "no"
-native_to            = "Air", "Missile", "Helicopter"
+native_to            = "Air", "Missile", "Helicopter", "Icebreaker"
 flags                = "NoCities", "NoBarbs", "NoPollution", "UnsafeCoast", "NoZoc", "NoFortify", "Frozen"
 property_ocean_depth = 32
 color.r              = 200
@@ -1121,7 +1121,7 @@ graphic              = "floor_ice"
 graphic_alt          = "arctic"
 identifier           = "V"
 class                = "Oceanic"
-movement_cost        = 1
+movement_cost        = 2
 defense_bonus        = 0
 food                 = 0
 shield               = 0
@@ -1148,7 +1148,7 @@ warmer_wetter_result = "Deep Ocean"
 warmer_drier_result  = "Deep Ocean"
 cooler_wetter_result = "no"
 cooler_drier_result  = "no"
-native_to            = "Air", "Missile", "Helicopter"
+native_to            = "Air", "Missile", "Helicopter", "Icebreaker"
 flags                = "NoCities", "NoBarbs", "NoPollution", "UnsafeCoast", "NoZoc", "NoFortify", "Frozen"
 property_ocean_depth = 87
 color.r              = 200
@@ -3376,7 +3376,7 @@ rmact_gfx      = "None"
 rmact_gfx_alt  = "-"
 buildable      = FALSE
 defense_bonus  = 50
-native_to      = "Sea", "Trireme"
+native_to      = "Sea", "Icebreaker", "Trireme"
 conflicts      = "River"
 ; /* xgettext:no-c-format */
 helptext       = _("\
diff --git a/xpt/units.ruleset b/xpt/units.ruleset
index ee504fa..f6a10fd 100644
--- a/xpt/units.ruleset
+++ b/xpt/units.ruleset
@@ -146,6 +146,14 @@ min_speed     = 2
 hp_loss_pct   = 0
 flags         = "DamageSlows", "AttackNonNative", "AttFromNonNative"
 
+[unitclass_icebreaker]
+; /* TRANS: Unit class: used adjectivally */
+name          = _("?unitclass:Icebreaker")
+min_speed     = 2
+hp_loss_pct   = 0
+flags         = "ZOC", "DamageSlows", "AttackNonNative", "AttFromNonNative", "TerrainSpeed"
+; FIXME: TerrainSpeed => slow out of port
+
 [unitclass_trireme]
 ; /* TRANS: Unit class: used adjectivally */
 name          = _("?unitclass:Trireme")
@@ -1758,7 +1766,7 @@ The Battleship is the supreme naval unit with\
 
 [unit_submarine]
 name          = _("Submarine")
-class         = "Sea"
+class         = "Icebreaker"
 tech_req      = "Combustion"
 obsolete_by   = "None"
 graphic       = "u.submarine"
@@ -1791,6 +1799,41 @@ Traveling under the surface of the ocean, Submarines have\
  off guard.\
 ")
 
+[unit_icebreaker]
+name          = _("Icebreaker")
+class         = "Icebreaker"
+tech_req      = "Nuclear Power"
+obsolete_by   = "None"
+graphic       = "u.icebreaker"
+graphic_alt   = "u.dredger"
+sound_move    = "m_icebreaker"
+sound_move_alt = "m_generic"
+sound_fight   = "f_icebreaker"
+sound_fight_alt = "f_generic"
+build_cost    = 100
+pop_cost      = 0
+attack        = 0
+defense       = 3
+hitpoints     = 30
+firepower     = 1
+move_rate     = 4
+vision_radius_sq = 8
+transport_cap = 2
+fuel          = 0
+uk_happy      = 1
+uk_shield     = 1
+uk_food       = 0
+uk_gold       = 0
+cargo         = "Sea"
+flags         = "BadCityDefender", "Only_Native_Attack", "HasNoZOC"
+roles         = ""
+helptext      = _("\
+An Icebreaker can escort up to two other ships through polar ice \
+in a tight convoy (by transporting them). Icebreakers move slower through \
+ice than open water.\
+")
+; FIXME: this model of escort gives escorted ships free extra movement
+
 [unit_carrier]
 name          = _("Carrier")
 class         = "Sea"