http://www.rockislandauction.com/viewitem/aid/66/lid/3479

Most everyone is familiar with the Luger pistol - it is one of the most iconic handgun designs ever made. Folks who have a passing interest in the guns will probably know about both the standard Army model (the P08) and the long-barreled Artillery model (the lP08, with its shoulder stock and snail drum magazine accessories).

What a lot fewer people know about is the third major German military version of the Luger; the P04 Naval version. The Germany Navy was looking to replace its long-obsolete Reichsrevolvers at the same time the Army was, but while the Army was also dealing with the expense of adopting the new Mauser 98 rifles, the Navy needed far fewer pistols and had a budget on hand to buy them. They took the German Army and Swiss Army trials reports at face value and adopted the 1904 pattern Luger in 1904.

These pistols had 6 inch long barrels (compared to the 4 inches on Army models), rear sights adjustable for 100 or 200 meters, and they came with shoulder stocks for making the guns into convenient carbines. They were purchased in batches starting in 1904 (although the first deliveries took almost 2 years) and running through the end of World War I.