The Martini action is a single-shot falling block firearm action that was actually invented by an American named Peabody. The US showed no interest in the Peabody action so he offered it to other nations. A demonstration was made in Switzerland, and the Swiss, being who they are, incorporated some improvements to the Peabody design. The Swiss gentleman involved was named Martini and the action became known as the Martini action. The Martini action was adopted by the British Army with great success. It's most public exposure is probably in the movie "Zulu" where it is shown in detailed operation.
The major difference between the Peabody action and the Martini action is that the Peabody action used a manually cocked external hammer whereas the Martini action uses an automatically cocked internal striker mechanism - a tremendous improvement.
The Martini action has been used in pistols, flare guns, marine rope throwers, harpoon guns, shotguns and rifles in all calibers from 22 to 577.