Why is an anachronistic modern conjugation thrown into the lyrics of 軍艦行進曲?

Question

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?

Answer 1

This looks like modern "浮かべる" but it is actually classical "浮かぶ" (四段, "to float") plus what is traditionally taught as the "り" auxiliary verb (助動詞).

Etymologically, of course, it is really just "ari" attached to the ren'yokei 連用形/infinitive: /ukabi/ + /ari/ = /ukab(y)eri/, /ukab(y)eru/ adnominally (as in this case). Frellesvig calls this the "morphological stative".

So, in terms of meaning, this 浮かべる is roughly equivalent to contemporary 浮かんでいる.