Technically, boilermakers manufacture boilers and storage tanks, but the term is also used generally to refer to any craftsman who works with sheet iron or steel, including in the building of ships, boats, barges, bridges, gasometers, etc. These men all tended to belong to the same unions.

Note that boilermakers and other workers on the railways usually belonged to the railway unions instead of to trade-specific unions.

United Society of Boilermakers and Iron Shipbuilders and successors

The main union for boilermakers and one of the two main unions for shipbuilders, this union was formed in 1852 by the amalgamation of the Scottish Society of Boilermakers, the United Friendly Boilermakers' Society and the Amicable and Provident Society of Journeymen Boilermakers (no archive material is held for these predecessor unions). It went through several incarnations:

• United Society of Boilermakers and Iron Shipbuilders (1852-1898)
• United Society of Boilermakers and Iron and Steel Shipbuilders (1898-1953)
• United Society of Boilermakers, Shipbuilders and Structural Workers (1953-1962)

This union always admitted boilermakers, platers, riveters, holders-up, caulkers and anglesmiths. By 1912 it admitted draughtsmen working on shipbuilding and iron and steel construction. By the 1950s (and maybe before) it was also admitting other skilled shipyard workers and workers in similar industries, including drillers and steel erectors. It had branches throughout Great Britain and Ireland, and also in the first quarter of the 20th century in South Africa, Malta and Gibraltar.

Genealogical sources exist from 1871 to 1962.

Associated Shipwrights' Society and successors

The other of the two main unions for shipbuilders, it was formed in 1882 by the amalgamation of a number of small local unions. It too went through several incarnations:

• Associated Shipwrights' Society (1882-1908)
• Shipconstructive and Shipwrights' Association (1908-1912)
• Shipconstructors' and Shipwrights' Association (1912-1963)

It seems to have initially only admitted those specifically rated as shipwrights, in wood as well as metal, and also admitted drillers and hole cutters. It later expanded its remit somewhat and even started admitting sailmakers from 1920, but it did not admit boilermakers and only seems to have recruited in the shipbuilding industry.

Genealogical sources exist for the entire history of the union.

Smaller unions

The United Society of Boilermakers and Iron and Steel Shipbuilders absorbed the Sheet Iron Workers' Society in 1920. This union operated in Scotland and Northern England.

The Shipconstructive and Shipwrights' Association absorbed three smaller unions:

• United Society of Drillers, operating in London, in 1908.
• Wear Shipwrights' Benevolent Society, operating in Sunderland and area, in 1908.
• Amalgamated Society of Drillers and Holecutters, operating in Hartlepool, Stockton-on-Tees and area, in 1910.

There are lists of members of all these unions on amalgamation, but nothing from before this time.

United Society of Boilermakers, Blacksmiths, Shipbuilders and Structural Workers and successors

In 1962, the United Society of Boilermakers, Shipbuilders and Structural Workers amalgamated to form the United Society of Boilermakers, Blacksmiths, Shipbuilders and Structural Workers. In 1963, the Shipconstructors' and Shipwrights' Association amalgamated with this union to form the Amalgamated Society of Boilermakers, Shipwrights, Blacksmiths and Structural Workers. Since then all shipbuilding and structural workers have belonged to the same union, which amalgamated again to become the General, Municipal, Boilermakers and Allied Trades Union (GMB) in 1982.

Genealogical sources exist from 1962 to 1984.