There are more questions than answers about the A/6538. The few examples that have appeared all share the same unusual characteristics. Not one of them has a serial number; all have the previously unknown model number 6540 stamped inside the case back and then carefully crossed out. All bear the manufacturing stamp for the third quarter of 1957; all have most unusual bezels and Explorer-style 3/6/9 dials. These were the first Rolex military Submariners; they were issued only to the elite Special Boat Squadron of the Royal Marines (the inspiration for the US Navy SEALS). The case has rudimentary fixed bars; the caseback has full military markings and is further marked by many years of a nylon G10 strap being in the same position. It seems that in 1961 the British Ministry of Defence ordered that all dials using radium be withdrawn and replaced by dials using tritium. The present watch retains its original dial due to the fact that it was lost on the beach. The story is interesting: a beachcomber with a metal detector found it buried beneath a foot or more of sand on his local beach. Unbelievably, the Oyster case had protected the watch from the action of the tide for over 40 years, keeping the movement dry and clean. The original glass was completely opaque as the sand being washed over it with the tides had acted like fine sandpaper. However, the glass required only the lightest of polishes before it sparkled like new.