As he is beginning to mull over the actual requirements needed to make a submarine functional, that hollow feeling he has not missed sweeps through him. His head lowers forward as his eyes close and he brings a hand to his head. A resounding heartbeat injects a new memory into his mind. Donatello had made a submarine of his own, and on the first trip out into the ocean he found trouble of a rather revolting nature.

Hand lowered from his head to shake his head clear, he picks up the waiting note he had failed to catch and writes.

Sorry about that. Got another memory. Donatello made a submarine. At least it gives me a place to start with design.

A base would be beneficial. Directly on the water may be dangerous and limits options somewhat, but any base would be nice to have . An underwater tunnel or cavern might suffice to hide a small submarine if I can manage it.