During the late 1960s, in collaboration with COMEX, Rolex developed its ?Submariner? model to meet the most stringent technical and professional demands. COMEX divers not only needed solutions for water resistance at extreme depth, they also faced the danger of explosive decompression caused by helium penetrating the interior of the watch while they breathed the mixture of oxygen and helium within their hyperbaric chamber. To maintain a pressure identical to that underwater, the mixture in the hyperbaric chambers remained the same during the different phases of work and rest periods. This system was designed to eliminate the need to depressurize the chamber after each phase of work. Before returning to free air, and depending on the depth attained, a period of depressurization was necessary to equalize the internal and external tension of the human organism. Though the process of depressurization is slow, the gas that accumulated inside the watch, having no means to escape fast enough, exploded the crystal thereby risking injury to those inside the chamber. Rolex collaborated with COMEX to develop a solution by installing a one-way pressure escape valve on the side of the watch case, beside the nine o'clock position. The one-way valve began to function when the difference between the exterior and interior of the watch exceeded 2.5 kg. per sq. cm. The Helium Gas Escape Valve (HEV) was featured and tested on the Single red and Double Red Patent Pending Sea-Dwellers circa 1967-1969. Once the testing was successfully completed and Patent of the HEV approved, COMEX placed a special order with Rolex for the supply of a number of dive watches featuring the HEV and case with either ref. 5513 or 5514. This would be delivered to COMEX only and not provided for general sale. The development and delivery of this unique reference evolved from a modified ref. 5513 to the final ref. 5514 with big case back numbers circa 1975. The first COMEX deliveries were the Submariner ref. 5513, which can be found in a number of iterations: 1- The earliest ref. 5513 COMEX watches that have surfaced circa 1969/70 have non-HEV cases, non-logo dials and case backs which are engraved ?Crown-Rolex-Comex?. The serial number engraved inside the case back matches the serial number between the lugs at 6 o?clock. 2- The ref. 5513 COMEX watches with HEV (an improved version introduced post Patent approval) that followed circa 1972 were mostly produced with a small or medium sized issue number engraved on the case back and a plain matt non-logo dial. Approximately only one third of the original issued ref. 5513 COMEX watches had a matt logo dial and very few have survived. Thus making the ref. 5513 with the original COMEX logo dial configuration, one of the rarest COMEX watches to exist (estimates have been made in the region of 50-60 watches). The present watch has recently been serviced by Rolex and comes with a letter from Rolex confirming its original delivery to COMEX.