A lack of sailors has meant four British warships have not spent a day at sea in 2018, new data have revealed.Responding to a parliamentary question, the Ministry of Defence figures show the effect on Britain’s Type 23 fleet due to ageing hulls and under manning.A National Audit Office report in April showed that the Royal Navy suffered a manpower shortage of 16 per cent in 2016/17.First commissioned in 1989, the Type 23 Frigates have a planned 18-year lifespan which has been regularly extended. As they age the frigates need more time in maintenance as systems require updating or refitting.The fleet is due to be replaced by eight Type 26 ships, the first of which is currently under construction in Scotland. Increasing naval deployments from six to nine months due to the lack of sailors has meant that ships are alongside for greater periods before the tour, to allow service personnel time with their families. In turn this means a longer maintenance period is required at the end. The ships are also in port for about two weeks in the middle of a deployment for crew leave. Want the best of The Telegraph direct to your email and WhatsApp? Sign up to our free twice-daily Front Page newsletter and new audio briefings. Post-deployment each frigate will revert to a very low readiness state. The Daily Telegraph understands that a number of training exercises in UK waters now happen from Monday to Friday, allowing servicemen and women to go home at weekends and shortening the overall time ships spend at sea.A government review of defence in 2010 saw 5,000 naval servicemen and women made redundant, and the UK’s overall defence budget reduced by 7.7 per cent over four years.New data show that the UK’s thirteen frigates have spent a total of 817 days at sea in the period to Oct 1. Between 2010 and 2014, the ships were at sea for at least 1500 days each year.HMS Argyll and HMS Sutherland have spent the longest at sea this year, with 117 and 154 days respectively.Admiral Lord West of Spithead, a former Labour security minister, told The Daily Telegraph that funding cuts were making recruitment and retention of staff more difficult for the Navy.“There’s no doubt that the hollowing out of the military is causing a lot of problems,” he said.“People aren’t doing the things they thought would happen when they joined up, and they’re saying ‘to hell with this’ and they’re going to go.”“We need all these ships operating. There are jobs for them to do around the world, and when they’re doing those jobs it helps stabilise things and helps keep peace”. HMS Portland is seen on the Atlantic Ocean, near Ascension Island. MoD data have shown that the Frigate is one of four in Royal Navy service that have spent no days at sea in 2018.Credit:Reuters A Royal Navy spokesman said: “Type 23 frigates are true workhorses across the globe, as shown by current operations with HMS Monmouth in the USA and HMS Argyll in the Far East.” Each costing about £130 million, the Type 23 frigates are all named after British Dukes and are known as ‘Duke Class’. Based in Portsmouth and Devonport the primary role of the ships is anti-submarine warfare, through the use of a towed array sonar which trails behind the ship, electronically listening for emissions from submarines.The data show that since 2010 the entire Type 23 fleet has spent a total of 32.5 years at sea. Assuming a crew of 185 sailors this equates to roughly 2.2 million man-days. On average that means each frigate has spent around 28.5 per cent of its time at sea annually. This figure will vary widely depending on the role of the vessel at the time and serviceability state.However, ‘days at sea’ can be an unhelpful metric when assessing the value to the taxpayer. Many tasks require a serviceable ship to be in port. For example, the Fleet Ready Escort role requires a ship to be available for immediate tasking, such as for escorting Russian warships through the Channel.Ships on deployment will also spend many days in port for maintenance, replenishment or to host visitors and foreign VIPs. Many UK defence sales come from such engagements.