A shipfitter is a marine occupational classification used both by naval activities and among ship builders; however, the term applies mostly to certain workers at commercial and naval shipyards during the construction or repair phase of a ship.

Ther term is derived from the words "ship" and "fit" -- essentially, "fitting" parts of the "ship" together.

Naval usage

A shipfitter is an enlisted or civilian person who works on heavy metal

Heavy metals

A heavy metal is a member of a loosely-defined subset of elements that exhibit metallic properties. It mainly includes the transition metals, some metalloids, lanthanides, and actinides. Many different definitions have been proposed—some based on density, some on atomic number or atomic weight,...

 like high-tensile steel, high yield strength steel, etc.

Shipfitters fabricate, assemble and erect all structural parts of a ship, coordinate all fixed tank work performed on submarines and ships, and coordinate all sonar dome work. Shipfitters also use heavy machinery such as plate planners, shears, punches, drill presses, bending rolls, bending slabs, plate beveler, saws, presses up to 750 tons, angle roll (vertical and horizontal), dogs and wedges. Shipfitters are responsible for hydro and air testing of tanks and compartments as well as perform grinding, drilling, and fit up operations on submarines and surface crafts.

Ship builder usage

A shipfitter is a worker who “fits” together the structural portions of a ship by either welding

Welding

Welding is a fabrication or sculptural process that joins materials, usually metals or thermoplastics, by causing coalescence. This is often done by melting the workpieces and adding a filler material to form a pool of molten material that cools to become a strong joint, with pressure sometimes...

 or by riveting.