Photos: Submersibles explore the deep

The three-person submersible Clelia is launched from an A-frame crane. The Clelia can cruise at 3 knots and is certified to operate at a maximum depth of 1,000 feet.

Scientists have maximum visibility in the Johnson-Sea-Link's acrylic sphere, which can accommodate four people, dive to 3,000 feet and travel at 1 knot.

Woods Hole Oceanographic Institution's autonomous underwater vehicle, the Autonomous Benthic Explorer (ABE). Developed in the mid-1990s, the ABE can be programmed to monitor underwater surfaces for months at a time, during which it takes photographs and collects surface samples and other data. It weighs 1,200 pounds and has a cruising speed of 2 knots.

The RCV-150, a remotely operated vehicle, as it is deployed from its steel cage. The RCV-150 is designed to operate as far down as 3,000 feet.

The Alvin, owned by the Woods Hole Oceanographic Institution, was the brainchild of Allyn Vine, a WHOI engineer who conceived of the submersible in the 1930s and later helped develop it. The first Alvin dove to 35 feet. As currently constructed, it can descend to 14,764 feet.