Windham William Sadler made the first successful aerial crossing of the Irish Sea, which he accomplished by balloon.

Windham William Sadler was an English balloonist. His father was aviation pioneer James Sadler and, after an education in engineering, Sadler followed in his father's footsteps. He made an ascent in London during the Grand Jubilee of 1814 and in 1817 made the first successful aerial crossing of the Irish Sea, a feat that had been unsuccessfully attempted by his father. Sadler was killed when his balloon crashed into a chimney near Blackburn during a flight in 1824.

The Irish Sea is a 46,007 km² (17,763 sq mi) body of water that separates the islands of Ireland and Great Britain. It is linked to the Celtic Sea in the south by St George's Channel and to the Inner Seas off the West Coast of Scotland in the north by the North Channel. Anglesey, North Wales, is the largest island in the Irish Sea, followed by the Isle of Man. The term Manx Sea may occasionally be encountered.