The British Army's patrolling challenge is back after last year's event was cancelled due to COVID-19.
Exercise Cambrian Patrol, organised and run by Headquarters 160th (Welsh) Brigade and based in Brecon, mid-Wales, starts on Friday and runs until 17 October.
Split into eight phases, the two-day patrolling mission is 37 miles, with troops carrying full personal kit and equipment.
During the patrol, teams of eight soldiers must deal with a number of specific scenarios involving enemy forces.
They must then battle prep and map out a designated route, which they must navigate through day and night, as well as tackle a number of stands.
This includes casualty evacuation scenarios, dealing with mock improvised explosive devices, intelligence gathering, seeking protective measures against chemical, biological, radiological and nuclear threats, a water crossing and close-target reconnaissance.
Watch: Meet the female team of Officer cadets on Exercise Cambrian Patrol in 2019.
Cambrian Patrol is the largest exercise of its kind in the world – with foreign entrants having to qualify for entry via their own domestic competition.
Depending on how the teams perform, they are awarded points for which they will either gain a gold, silver, bronze or certificate finish.
On average, only 5% of patrols gain the top award, while a third fail to finish.
Brigadier Andrew Dawes CBE, Commander 160th (Welsh) Brigade and Exercise Director, said he was "thrilled the exercise is back".
"The format remains focused on the battle craft syllabus to an annual training test standard," he said.
"One may think this sounds simple, but you would be quite wrong."
A mix of Regular, Reserve and University Officers' Training Corps teams will take part, plus nearly 20 patrols representing armies from across the globe.
Brig Davies added that "the exercise continues to evolve".
"This year a human performance monitoring study is taking place and the Army's Enhanced Light Force Battalion will trial new equipment prior to it coming into general service," he said.
"It remains a rite-of-passage event for our finest soldiers and is supported by more than 350 personnel from across the Army and dozens of contractors and Dstl scientists who support the Brigade in its delivery."
The number of patrols has been scaled back to a maximum of 100, down from 145.
The exercise had only been cancelled once before – in 2001, due to the Foot and Mouth disease crisis in cattle.