Although it may bring to English minds some awful toilet-related scenarios, that's not what a Boghammar is. The name comes from a company, Boghammar Marin AB, in Lidingö, Sweden. Boghammar was formed in 1906 (by the Boghammar family, natch) to build small boats - fishing boats, dinghys, etc. In 1928, Boghammar switched over to making only aluminum-hulled boats - a newfangled technology in high demand for said boats' light weight and strength.
They would have likely remained just another local brand had they not started making larger and faster boats and then made a fateful sale in the early 1980s to the navy of Iran. The boats sold to Iran were 6.4 ton very fast boats of around 13 meters in length with stepped-hydroplane hulls. They were bought for use as coastal patrol craft, and Iran promptly armed them with a mix of light weapons including recoilless guns, mounted machine guns, and RPGs or rocket launchers. Iran had, by 1987, some 37 of these boats.
During the Tanker War, Iran began using these boats (staging from offshore oil platforms) to harrass shipping proceeding through the Persian Gulf, especially the Strait of Hormuz, to and from Iraq. Although not heavily armed, they were more than fast enough to chase down merchant ships and had enough punch to threaten them with unacceptable damage. They were used for boarding as well as skirmishing with Iraqi light vessels. To Western navies, especially the U.S. Navy, these small, fast combatants were known as "Boghammar boats" or just "Boghammars."
In 1988, the U.S. frigate Samuel B. Roberts (FFG-58) struck a mine in the Gulf. It limped back to Dubai for repairs. Navy divers recovered additional mines in the area which had serial numbers indicating they were from the same lot as some mines that had been found aboard the Iranian minelayer Iran Ajr in September the previous year by U.S. forces when they intercepted the Ajr laying mines. As a result, the U.S. planned a retaliatory strike, which was code-named Operation Praying Mantis.
On April 18th 1988, a task force of U.S. warships engaged two Iranian oil platforms being used to coordinate shipping attacks, platforms Sassan and Sirri. Platform Sirri was set ablaze by bombardment; platform Sassan, despite losing its main structure to a fire after being struck by a TOW missile, was captured and boarded by Marines.
In response, the Iranians sortied several vessels including a patrol boat and several Boghammars. The patrol boat, the Joshan, fired a Harpoon missile at U.S. forces, who evaded and returned fire with Harpoons and Standard missiles, making this the world's first duel between missile-armed warships. The Boghammars attacked a Panamanian-flagged vessel, and President Reagan (via a satellite comm from the White House) authorized their destruction. A-6 Intruders from the USS Enterprise (CVN-65) standing further out in the Red Sea sank the Boghammars with cluster bombs.
Following this encounter with the Boghammars, the U.S. Navy adopted both the term Boghammar boat to indicate any small and fast craft fitted with light weapons, and the phrase Boghammar tactics to indicate the practice of sortieing fast light combatants from a safe harbor, striking shipping, and returning just as quickly. The term was later used for coastal defense tactics using diesel-electric submarines, in which the SSKs (going up against SSNs and ASW in deep water) remain in port except for quick dashes out when targets are within range.
Boghammar Marin AB remains in business, and in the early 1990s undertook to refit several of the Iranian Boghammars for them. Much like Chad's 'technicals' - Toyota pickup trucks with light weapons - the Boghammar has become the marine icon of inventive low-tech combat.
Sources:
Eric Wertheim, The Naval Institute's Guide to Combat Fleets of the World 15th ed. U.S. Naval Institute Press: Annapolis, 2007. (p. 327)
Bradley Peniston, No Higher Honor. U.S. Naval Institute Press: Annapolis, 2006.
Aerospace and Defense Source: http://www.asdsource.com/source_detail_small/3078/Boghammar_Marin_AB.htm.