I think the Royal Navy and RNPS acted in parallel around the UK – as I remember two Royal Navy ships working at exactly the same time during WWII – both holding exactly the same name of “HMS Beaumaris Castle” (but with different registration numbers). The point was that the war with Nazi Germany caught the UK government by surprise and there was not enough time (nor was there the resources) for the government to build proper military-grade mine-sweepers. Fishing vessels were acquired and thousands of volunteers called for to immediately defend the UK coastline. Those men who volunteered were permitted to “choose” to serve in the RNPS – rather than being placed wherever the government most needed men. The above extract sheds light on how the RNPS was first formed in 1939.