Especially made for the SBS (Special Boat Squadron) in the seventies and also known as MILSUB. An extra reason for joining the Royal Marines in that time. The case back has the Military broad arrow and the appropiate Military markings. Rolex Military submariners came from Geneva with the fixed bars and the special hands and dials but the Ministry Of Defense did the case back engraving. The spring bars were not fitted, the holes were drilled out and solid bars then hammered into place. The ends of the bars were then filled and polished so that they become almost invisible. When it became apparent that the MOD were going to order more of these watches, Rolex chose to give the new watches a distinct model number 5517. The MILSUB is highly treasured by the serious Rolex collector.