不沈 is read as ふちん (fuchin) and means unsinkable.
ふちん
fuchin
ふちんくうぼ
unsinkable aircraft carrier
ふちんかん
unsinkable battleship
ふきょう
depression
ふかのう
impossible
ふかけつ
indispensable
ふか
failing grade
ふきそく
irregularity
ふじゅん
irregular
ふかい
indisposition
ふかかい
incomprehensible
ふもう
unproductive (e.g. discussion)
impure