The top secret past of a sprawling complex of buildings hidden in the Welsh countryside

From a bird's-eye view, one grasps its vastness - a colossal complex composed of hundreds of buildings and large swathes of now mostly untouched and unused Welsh countryside.

Strangely enough, despite its enormity, it largely remains unknown to those residing outside its nearby radius about five miles west of Chepstow. This ex-Royal Navy propellant factory, located near the Monmouthshire village of Caerwent, boasts a remarkable history, including a past life manufacturing and storing munitions whilst housing various military forces.

Currently, it serves as a training ground and occasionally moonlights as a filming site for Hollywood movies or TV programmes. Images reveal the expansive scale of the location, which encompasses over 400 buildings and bunkers. It stretches two miles wide across 600 hectares, encircled by a perimeter road extending more than seven miles in length. For the latest Welsh news delivered to your inbox sign up to our newsletter

READ MORE: Derelict school still has artwork on the walls and PE kit on the floor

READ MORE: The truly bizarre plans for Cardiff that would have seen the city transformed beyond recognition

Originally, this site was dedicated solely to producing and storing Royal Naval munitions. Back in the summer of 1936, the plans for the Royal Navy were drafted. It required a location invulnerable to air raids, far removed from industrial areas yet conveniently close to a populous region that could provide an "adequate workforce", amongst other things.

Water from the Severn Tunnel, which would later become integral, was identified as a key feature leading to the selection of the site near Caerwent. Construction commenced in 1939, with the site reaching full operation by 1941 for the production of cordite for the Navy.

Between 1938 and the close of World War II, several Royal Ordnance Factories (ROFs) were launched across the UK. One of the first was set up in Bridgend, Wales - alongside others in Cardiff, Glascoed, Hirwaun, Newport, Pembrey, and Wrexham. These factories employed thousands of workers over time, with the munitions they crafted playing a key role in helping the Allies win WWII. When the Cold War kicked off, Caerwent pivoted to produce rocket boosters for Seaslug missiles - the era's first generation surface-to-air weaponry.

From 1957 onwards, various buildings were earmarked for different roles, including production and testing, with one building named J7 acting as an environmental conditioning site where temperatures could range from a sweltering 70C or be adjusted to a chilling -40C.

However, by 1966 it was decided that the site should be shut down as an armament works, at which point it transformed into bases for both British and US armies. The RAF Caerwent site was duly transferred over to US management after French President Charles de Gaulle prompted the exit of US military forces from France in 1967.

Later known as USADA Caerwant, the location became an integral part of the United States' "theatre reserve stocks", and was placed under the command of the US Army's 47th Area Support Group Reserve Storage Activity.

The US Army invested over £4 million in the construction of 300 gun magazines and the storage of small arms ammunition, artillery shells, grenades and flares. At its peak, Caerwent was one of the largest ammunition supply depots in western Europe, housing over 80,000 tonnes of conventional munitions, a significant portion of the US Army's European stockpile.

In 1990, Caerwent dispatched 12,000 tonnes of ammunition to the Middle East, playing a pivotal role in Operation Desert Shield and Desert Storm in Iraq. In June, 1992, the US army announced plans to shut down their storage operations at the Caerwent site. Over the course of 10 months, 60,000 tonnes of munitions were transported out of the site, with the final batch removed by train in July, 1993.

Today, the site is frequently used as a filming location for various films and TV shows. Scenes from the Hollywood blockbuster, Captain America: The First Avenger, were shot on site in October, 2010 and, more recently, it was featured in the television series, Top Gear.

It has also served as a filming location for an episode of Doctor Who titled, Before the Flood.