The reference 5517 is a special reference reserved solely for the Rolex Submariner made for the Special Boat Service of the Royal Marines. These watches were specially ordered from Rolex by the Royal Navy for use by the commandos of the British Special Boat Service, one of the world's most highly trained Special Forces. These watches all have fixed bar lugs which by stipulation of the British Ministry of Defense should not be less than 2 mm in diameter. The ref. 5517 had a unique bezel with sixty minute marks rather than only the first fifteen. Other stipulations were that the hands should be of sword type as they are more clearly legible under low light conditions, that the dials be marked with the 'Circle T' which signified that the dials used Tritium, and that the case backs be engraved on the interior with the case number to avoid backs being swapped during servicing, thereby rendering the issue mark invalid as the case numbers for all the watches are recorded against the issue number in the Quartermaster's register. The ref. 5517 was issued until the early 1980s when the contract with Rolex expired. It is believed that the total number of all British Military Submariners, both 5513 and 5517 models was just over 1,000, delivered in three batches.