If we are using the submarine, we might as well send our fully battle-ready catfishes to swim alongside it.
Veto until we have spare ones.
Reason for veto, they breed. Eventually. We must not get to many, but we have only these two. If we lose them we might never have more - and we have no other aquatic monsters that can breed as yet.
They are fully battle ready, but they are low on the 'battle chain', they would be among the first to die if there are losses in the battle (I believe they'd die next, after the cogs).
While I don't want to lose the next level of troops over them either, which are 'Gorloceros-Elephant Wraith-Figurehead' - I understand that none of those are directly reproductive.
The figurehead is actually 'easy' to replace if we want to, we summoned her with common materials. Elephant wraith was also summoned, but not with easily recreated materials (we used a lot of our nearly destroyed forces and damaged base and a few other things, right?)
Gorloceros is a mutation, mutations are largely one-shot deals and easily tried for if we have a base to mutate... they'll all be different and some won't survive the change, but given an army to mutate we'll end up with most of an army of mutants.
If we want more behemoth fishes, patience is the way to get them.
That said, maybe we should look into a fishnet and get some normal fish for the purpose of being the 'base' to mutate with giant catfish mutagen. Fish should be highly plentiful, many will survive, and some will surely be quite useful. Those one-shot mutations can swell our underwater ranks greatly if we desired.
Edited to add, I tentatively can support sending the baby behemoths, though I don't want to. Given plentiful fish in the sea (there's always more fish in the sea, right?) and huge reserves of giant catfish mutagen (essentially an infinite supply?... is it?... it sure is if we keep them alive but we might already have more than we could use in stock... do we?) we can maintain underwater forces even without our original force members... we started play with giant catfish (as well as Chemista and basic cogs).