In pictures: Royal Navy's new undersea surveillance ship set for military modifications

The first of the Royal Navy's new undersea surveillance ships has arrived in Birkenhead and is set to be turned into a 'mother ship' which will strengthen Britain's critical subsea infrastructure.

The ship, currently named Topaz Tangaroa, will have a period of military modifications which will include it being repainted, renamed, and have important military equipment installed.

The vessel will then take up its role as the first of two Multi-Role Ocean Surveillance (MROS) ships, operated by the Royal Fleet Auxiliary (RFA). She is due to be operational in the summer.

The 98m-long adaptable offshore patrol vessel, which is the length of Big Ben, will act as a 'mother ship’ and will be operated by remote and autonomous offboard systems.

With a weight of 6,000 tonnes, the vessel has a helipad, crane, an expansive working deck and features a 'moon pool' – a large access point in the underside of the hull through which submersible capabilities can be launched.

It will be crewed by about 24 RFA sailors, with 60 Royal Navy specialists operating the undersea surveillance systems.