軍艦行進曲 seems to be written mostly using Classical Japanese grammar. Here's the first stanza:
守るも攻むるも黒鐵{くろがね}の
浮かべる城{しろ}ぞ頼{たの}みなる
浮かべるその城{しろ}日{ひ}の本{もと}の
皇國{みくに}の四方{よも}を守{まも}るべし
眞鐵{まがね}のその艦{ふね}日の本に
仇{あだ}なす國{くに}を攻{せ}めよかし
Details like using the 連体形 なる in combination with ぞ, べし, 連体形 as a nominal in the first sentence, etc seem to be correct CJ grammar, and are more than the token き ending for adjectives and なり randomly thrown in J-pop songs so often. Obviously を and その are used in a very modern way, but most people aren't very familiar with を's old sense either.
However, 浮かべる stands out like a huge sore thumb to me. Clearly it should be 浮{うか}ぶる, the 連体形 of 浮{うか}ぶ? The song even gets 攻むる correct, and using 浮{うか}ぶる wouldn't disturb the meter in any way.
Is there some sort of reason, or is this just a random artistic choice? Usually songs are full of Modern Japanese and throw in Classical grammar for effect. This song is full of Classical gramamr and throws in a fragment of Modern grammar, for...effect?
Did 浮{うか}ぶ have an 一段 variant?