Building the Super Sub
Steve set out building a massive underwater "City like" structure so that he could bring most of his land dwelling friends down to the Ocean with him without developing many more super suits which would take more time.  He made the submarine equipped with cannons for defenses against the sea creatures of whom noone knew would be so terrifying.   He also built the superstructure on top of a very large platform to be sure that it was stable.  After that he equipped the submarine with large engines powerful enough to move it accross the waters at great speeds.