Submersibles are small research submarines like the German submersible Jago we used for 3 years to study coelacanths in Sodwana Bay.

Manned underwater vehicles used for research are generally referred to as submersibles to distinguish them from military submarines.

Military submarines generally do not have "windows" to look out of, whereas all submersibles do. Research submersibles are frequently able to go far deeper into the ocean than military submarines, as their smaller size makes it easier to create a tougher hull to resist the immense pressures of the deep ocean.

Manned submersibles vary considerably in size, construction, weight and how many people they can take. Most research submersibles take 2-3 people.

Much of the variation in construction depends upon the task they were designed to fulfill; submersibles which go very deep are generally made primarily of spheres of thick metal, either steel or titanium, with very small portholes made of very thick quartz glass or acrylic, like those used to study the very deep ocean, such as the famous submersible Alvin, well known for its role in the study of the mid ocean ridges and many other pioneering dives, the Russian Mir submersibles, which were used in the movie "Titanic", and the deepest-diving manned submersible currently operational, the Japanese Shinkai 6500, which is rated to 6,500m - note that the bottom of the ocean is over 11,000 meters and there is not a single manned vehicle operational today which can reach the bottom!

Submersibles designed to reach more moderate depths have considerably more variation in design. Some, such as the Johnson Sea-Link are made almost entirely of acrylic and offer fantastic almost wrap-around visibility. Submersibles with large viewports are generally restricted to more moderate depths. Jago, for instance, is rated to 400m, and has a large forward viewing port and a smaller dome at the top.

With the advances in materials and underwater technology, modern submersibles are smaller, lighter, safer and even more capable than in the past. The evolution of increasingly sophisticated manipulators (robotic "arms" and "hands") in particular has lead to an increase in the range of jobs which manned submersibles and ROVs can perform where previously a diver was required.

Both submersibles and ROVs can have a broad range of sampling equipment aboard. A primary function of underwater vehicles is taking video and still pictures. A range of cameras can be fitted, including traditional film cameras, digital video cameras, still cameras and low light cameras. Physical samples are also useful, and a range of sampling equipment such as manipulators and storage baskets and "slurp guns", sediment coring devices and submersible-deployable traps have been developed to sample organisms and the seafloor itself.

You may also like to read about ROVs.