Louis Brennan (28 January 1852 – 17 January 1932) was an Irish-Australian inventor. He was born in Castlebar moving to Melbourne, Australia in 1861 and starting his career as a watchmaker and a few years later was articled to Alexander Kennedy Smith, a renowned civil and mechanical engineer of the period.
He conceived the idea of a dirigible (in this case meaning steerable) torpedo in 1874, from observing that if a thread is pulled on a reel, the reel will move away. Brennan spent some years working out his invention, and received a grant of £700 from the Victorian government towards his expenses. He patented the Brennan Torpedo in 1877. The idea was trialled at Camden Fort near Crosshaven, County Cork.
In 1880 he went to England and brought his invention before the War Office. Sir Andrew Clarke alerted the authorities to the possibilities of the torpedo if used in the defence of harbours and narrow channels, and the patent was eventually bought for a sum believed to be more than £100,000. In 1887 Brennan was appointed superintendent of the Brennan torpedo factory, and from 1896 to 1907 he was consulting engineer.
He did much work on a monorail locomotive which was kept upright by a gyrostat. In 1903 he patented a gyroscopically-balanced monorail system that he designed for military use; he successfully demonstrated the system on 10 November 1909, at Gillingham, England, but fears that the gyroscopes might fail prevented adoption of the system for widespread use
From 1916 to 1919 Brennan served in the munitions inventions department.
From 1919 to 1926 he was engaged by the air ministry in aircraft research work, and gave much time to the invention of a helicopter. The government spent a large sum on it, but in 1926 the air ministry gave up working on it, much to Brennan’s disappointment.
In January 1932 he was knocked down by a car at Montreux, Switzerland, and died on 17 January. He married Anna Quinn in 1892 and she died in 1931. He was survived by a son and a daughter. Brennan was created a Companion of the Order of the Bath in 1892.
Gillingham library retains the archive of his papers.