Unnecessary; they already had a working cruise missile:
http://en.wikipedia.org/wiki/Henschel_Hs_293
with an impressive record of ships damaged and sunk to its credit. The difficulty was getting it near the target in the face of Allied air superiority.
The attack on HMT
Rohna is a fair example of its effectiveness. The ship was struck on the port side of the engine space by a single Hs293 which knocked a forty foot diameter hole in it, then detonated in the engine space, completely wrecking it and several decks above and blowing an equally large hole in the starboard side. The
Rohna sank a few minutes later. In spite of the fact that the other vessels of the convoy promptly came to their aid and that they were only a mile or so from the North African coast of the more than 4,000 aboard nearly 1,000 were killed and an equal number injured.