RNAD Trecwn RNAD Trecwn is a decommissioned Royal Navy Armaments Depot , located south of Fishguard in Pembrokeshire , West Wales . Built in 1938 to store and supply naval mine s and munitions ordance to the Royal Navy , at its height during the cold war 400 permanent workers were deployed at the site , housed in an MoD built town infrastructure . The site had an onsite narrow gauge railway , built using copper to reduce sparks . The weapons were both delivered to the site and then distributed using standard gauge rail to Fishguard , Neyland for Milford Haven , and latterly Pembroke Dock . Decommissioned in 1992 , all 58 cavern storage bunkers and the extensive above ground network of storage sheds and other military buildings remain in place . Ownership of the site was transferred from the Ministry of Defence to Anglo - Irish consortium Omega Pacific in 1998 , and then by court order to Hampton Trust in 2002 . The site is being redeveloped as an industrial park . Construction . Located on the former North Pembrokeshire and Fishguard Railway , south of Fishguard , construction was commenced in 1938 . Its location allowed supply of naval mines and munitions via rail from the West Wales Lines Fishguard branch , and distribution via a series of local deep sea ports , including Fishguard harbour and Neyland for Milford Haven . As with all munitions depots , safety and particularly planning for explosion prevention and firefighting was a major priority at the depot . The site used a specific design of narrow gauge railway for on - site distribution to minimise manual handling . For fire fighting two reservoirs are built into the hillside on opposite sides of the valley to supply high - pressure water to the onsite fire hydrant s , which are located both within each of the 58 stoarge chambers and alongside each surface building . Due to its scale and location , the MoD built a whole new infrastructure around the existing village to support the depot , with workers transported in , due to the remote location . This included three separate housing estates ( still occupied today ) , and a waste water treatment plant . Nearby Barham primary school [ built in 1877 with funding from the Barham family ] , closed in 2001 due to falling registers , after the RNAD closed . Layout and operations . The depot has a traditional herringbone layout along the valley , giving access to 58 cavern - based storage chambers , each approximately in length , which have been hewn into the rock of the valley sides . Each cavern storage chamber can be accessed either via road , standard gauge rail or the sites own narrow gauge railway . Munitions would be brought onto site mainly via standard gauge rail , and then distributed onsite using the specifically designed narrow gauge railway . Road access was mainly used for non - explosive access such as for workers and contractors , although it was occasionally used for supply and distribution . Distribution was via standard gauge rail using either Great Western Railway or British Railways locomotives hauling MoD / Royal Navy private owner wagons directly to Fishguard harbour , or Neyland for Milford Haven . After the closure of the RNAD sub - depot at Pembroke Dock , the Trecwn site gained additional workers and a longer distribution chain . At this high point of operations during the cold war , it employed up to 400 direct workers . Transport access . Purposefully located on the former North Pembrokeshire and Fishguard Railway , it gave the site easy access to excellent rail distribution . Direct passenger access was also provided by rail , with workmens trains reversing in from the Fishguard and Goodwick railway station until 1 August 1964 . Standard gauge . Just south of the main entrance and main security fence stands a single railway platform , for workers access to the site . Within the security fence , the marshalling yard of 8 parallel loops exists , formerly shunted by a dedicated MoD diesel hydraulic shunting locomotive . The line then extends down the valley , through a gauge exchange shed for access to the narrow gauge infrastructure , and then provides direct access to the 58 cavern storage chambers via a series of herring - bone shaped sidings . Supply trains would run from the site to both Fishguard harbour , Neyland for Milford Haven , and Pembroke Dock . At Fishguard the line extended beyond the ferry terminal at Fishguard Harbour railway station , continuing along the breakwater to a single line spur , allowing for transfer of munitions to Royal Navy ships . Narrow gauge . A narrow gauge line traverses the entire site , with direct access to the 58 cavern storage chambers . All rail infrastructure was built in copper to reduce the risk of sparks . Serviced via its own on - site locomotive shed and works , the line was equipped with a series of specially provided wooden enclosed wagons , with sliding roof covers . This allowed sea mines and other munitions to be directly placed within the wagons from overhead gantries , and transported over the entire site without access via any form of side door , hence enhancing safety . The narrow gauge line therefore became the main method of on - site distribution , with standard gauge rail or road the off site access method . Road . Connected to the A40 road via a private access road , the link gave access to both workers , suppliers and the occasional munitions delivery and distribution . Sale , current use . In the early 1990s , Trecwn was placed on care and maintenance by the MoD . The entire site was sold to Anglo - Irish consortium Omega Pacific in 1998 for £329 , 000 , with a stated intention of using the surface buildings for aircraft engine maintenance , while the underground caverns would be used for the storage of low - level nuclear waste . However , a lack of planning consent ( noise of the engines , level of radiation ) , and local opposition meant that the company ended up in court in 2002 , and was ordered to sell the site to Hampton Trust within 10 weeks . Hampton Trust intend to develop the site as a multi - use industrial estate , with the surface buildings rented or leased for light industrial purposes , and the caverns for storage and distribution . Network Rail have not only kept the railway connection operational , but refurbished it to allow the site to develop as an Intermodal freight traffic distribution site from Fishguard . Much of the narrow gauge infrastructure and stock remains in place , and maintained . Some stock has been transferred to the similarly gauged Welshpool and Llanfair Light Railway , and other items to the Talyllyn Railway and the Welsh Highland Heritage Railway . In late 2011 , Renewable Developments Wales applied for planning permission to build a diesel - powered peaking plant on of land close to the former main entrance . The plant is planned to produce 20MW of electricity using 11 generators , each stored within its own soundproof container .