In 1781 he received a commission in the Hanoverian guards, and as a captain took part in the campaigns of 1793-1795 in the Low Countries, distinguishing himself particularly on the Lys in command of light infantry. In 1803 the Hanoverian army was disbanded, and Alten took service with the King's German Legion (KGL) in British pay. In command of the light infantry of this famous corps he took part with Lord Cathcart in the Hanoverian expedition of 1805. He also fought at the Copenhagen in 1807.