母艦 is read as ぼかん (bokan) and means mother ship.
ぼかん
bokan
こうくうぼかん
aircraft carrier
すいじょうきぼかん
seaplane carrier
せんすいぼかん
submarine carrier
ぼたい
womb
ぼたいほごほう
Maternal Health Act
ぼけいせい
matriarchy
ぼけいかぞく
matrilineal family
ぼしかんせん
mother-to-child infection
ぼせいいでん
maternal inheritance
ぼしてちょう
maternal and child health notebook
ぼしけんこうてちょう
ぼけい
maternal line