submersible

A submersible is a watercraft designed to operate underwater. Unlike a submarine, which is typically capable of prolonged independent travel, a submersible usually relies on a surface vessel or support platform for launch and recovery and has limited endurance underwater. Submersibles may be crewed or unmanned.

Types include manned submersibles, remotely operated vehicles (ROVs), and autonomous underwater vehicles (AUVs). Manned submersibles carry a small crew inside a pressure hull; ROVs are tethered and controlled from a surface ship; AUVs operate on pre-programmed missions without real-time human control.

Core design elements are a pressure hull able to withstand external water pressure, ballast systems for descent and ascent, propulsion and thrusters for maneuvering, and observation means such as viewports or cameras. Manned vehicles require life support and redundancy for critical systems.

Historically, submersibles enabled deep-sea exploration in the mid-20th century. Notable milestones include the Trieste reaching the Challenger Deep in 1960, Alvin's ongoing work since the 1960s, and James Cameron's 2012 Deepsea Challenger dive. Modern submersibles support science, archaeology, and industrial inspection.

Applications span oceanography, marine biology, underwater archaeology, salvage, offshore construction and maintenance, and military reconnaissance in some cases. They complement surface vessels in environments too deep or dangerous for divers.

Operational safety hinges on depth ratings, life-support reliability for manned vehicles, redundancy, training, and adherence to applicable regulatory standards. Deployment typically requires a support vessel, trained pilots or operators, and mission planning.