The Secret of Two Oceans

The story

The enemy agents from an unknown nation have secret automated facilities set up in the Atlantic and Pacific oceans for the purposes of sinking ships. The super submarine "Pioneer" and it's intrepid crew is dispatched to find the source of these mysterious sinking's...Unknown to the captain, his chief engineer is working for the bad guys, intent on stopping their efforts, at any cost...

It seems the real chief had a twin brother who was a circus acrobat who murdered and replaced him.