A genuine Admiralty Pattern 300 pocket watch, c.1940. Presented in full working order, despite the battle-scarred appearance.The Admiralty Pattern 300 is a favourite among military watch collectors, but its precise purpose has eluded historians, although clues and anecdotes exist that may help define the watch's wartime roles. To that end, some of what I now know about this watch is shared here.AP300 watches are robust in design, featuring a three-piece heavy-duty case that holds a 15-jewel Swiss Vertex or Aristo movement. Interestingly, identical Vertex watches were also trusted by British railway companies. No doubt, given the high number of 'Vertex 30' watch movements procured by the armed forces, it would be reasonable to assume that these were regarded as a 'value for money' option. Perhaps this was a serious consideration, especially if the AP300s were to face hazardous working environments, limiting their life expectancy. Today, many examples of the ubiquitous GSTP watches can be found and even the HS3 deck watches would appear to be plentiful, but the AP300 watches, while not rare, turn up in even smaller numbers.Fascinatingly, on Tapatalk, a contributor posted an Admiralty document from early WW2 stating that the AP300 was a 'Chartroom Watch'. However, the contributor was probably unaware that, while not every Royal Navy ship has a chartroom, H.M. Submarines do - The Chartroom being a dedicated area used for the storage of maps and a place where navigators would work undisturbed, plotting positions and courses.Both Vertex and Aristo supplied unbranded AP300 watches during the early war years. This was possibly due to the Swiss' concern of nazi retribution for assisting the Allies. After all, they were supposed to be neutral. Thinking tactically about supply and where demand was greatest, such as in the Atlantic convoy routes, it comes as no surprise that Aristo took the logistical step to open a watch agency in the USA. This move allowed the Swiss maker Aristo to import their AP300 watches before America joined the war. Those watches have their cases marked as being supplied by the 'Aristo Import Co.' and some additionally bear a tiny 'AXA' engraving on the balance bridge. The letters simply mean taxes have been paid by Aristo @ Aristo Import Co. but more importantly, they identify the machinations of the watch industry as they go about business during war.Furthermore, during conversations with the Combined Ops Pilotage Parties museum, it came to light that reports show their personnel carried AP300 pocket watches. COPPists, as they were routinely called, were responsible for reconnoitring enemy coastlines by kayak and, as a secondary objective, were responsible for acts of sabotage around ports... All very 'Cockleshell Heroes'. Such clandestine operatives typically arrived by submarine before setting off in their kayaks, so perhaps they too discovered the benefits afforded to them by the AP300 watch. Only other postwar documents that I have mentioned the GSTP as being the type used by COPP, or perhaps they used both.I hope that the information about these very solid watches provokes some thought. If you have any further information on the subject of the AP300, I would be delighted to hear back from you.Linked to the AP300, a near identical watch exists in the Royal Navy's inventory. Designated as the HS5, this watch differs in the dial configuration, where Arabic numerals are used, while the AP300 uses Roman numerals. The HS5 watches are attributed to use on survey vessels.