HMS Magpie, the third smallest commissioned vessel in the Royal Navy, has arrived in Portsmouth to begin a busy summer programme of survey work to ensure the harbour remains safely passable as homeport for the two Queen Elizabeth class carriers.

The task, the second since the vessel commissioned last year, picks up on the legacy of her predecessor HMS Gleaner which spent the latter years of its career scouring every inch of Portsmouth Harbour ahead of the arrival of HMS Queen Elizabeth. The small survey ship has recently completed a similar analysis of the waters around the BAE shipyard at Barrow to ensure the safety of the navy’s newest nuclear submarines.

Preparing the harbour for the new 65,000 tonne warships involved dredging and shifting more than three and a half million cubic metres of clay, sand and gravel as part of £100m worth of improvement works. With the second carrier, HMS Prince of Wales, due to arrive later this year the Harbour Board and Royal Navy are not taking any chances in ensuring the stability of the seabed.

The catamaran is well equipped for this with her built-in and towed sonar systems able to collect 800 readings per second to build a 3D image of the seafloor. With the sonar’s alone expected to gather half a terabyte of information it is no surprise that half her crew will not actually be on board during the survey mission. With four manning the vessel, the remaining half a dozen crew will be working from computers at Fort Blockhouse in Gosport to process and analyse the vast quantity of data as its collected.

“One of the biggest challenges is how busy the harbour is,” explained Commanding Officer Lieutenant Commander Will Alexander.

“There are around 230,000 movements every year, and it’s especially busy in the summer with pleasure craft. Being in command of Magpie is a hugely rewarding job…what we do has a direct impact on the ships and submarines of the Fleet, surveying waters so that they can use them safely.”

Magpie’s role in support of the combat arm of the fleet was further emphasised prior to this mission when the ship received its battle honours board, donated by shipyard Atlas, and commemorating the service and achievements of her eight namesake predecessors including the Second World War-era frigate famously commanded by the Duke of Edinburgh.

The ship will also support heritage and conservation efforts once work inside the harbour and main approaches is finished. This will include investigating the wreck site of Henry VIII’s flagship Mary Rose to see if there are any significant remnants left as well as a nearby wreck of a French Galley off the coast of the Isle of Wight.