In this vintage photo from 1983, we see crew members of the HMAS Onslow barbecuing a healthy amount of sausages on top of the submarine while it is still moving! The photo was scanned and posted to reddit by shanbuscus, whose father took the photo.

HMAS Onslow was one of six Oberon-class submarines operated by the Royal Australian Navy (RAN). The submarine was named after the town of Onslow, Western Australia, and Sir Alexander Onslow. Onslow was laid down at the end of 1967 by Scotts Shipbuilding and Engineering Company in Scotland, launched almost a year later, and commissioned into the RAN at the end of 1968. She was decommissioned in 1999, and was presented to the Australian National Maritime Museum, where she is preserved as a museum ship. [source]