Library image: Yui Mok/PA Wire.
Two SAS soldiers face trial by court-martial over the deaths of three reservists on a 16-mile march in the Brecon Beacons.
The men, known only as 1A and 1B, both deny "negligently performing a duty" by failing to take reasonable care for the health and safety of the candidates taking part in the exercise.
Lance Corporal Craig Roberts and Lance Corporal Edward Maher were pronounced dead on the Welsh mountain range after suffering heatstroke in July 2013.
Corporal James Dunsby died at Birmingham's Queen Elizabeth Hospital from multiple organ failure more than two weeks later.
1A and 1B, whose identities are protected by an anonymity order, appeared behind a screen at Colchester Military Court on Monday accompanied by their barrister Lewis Cherry.
Their names, ranks and numbers were supplied to the judge in writing.
1A, a serving captain who was the training officer in charge of the march, and 1B, a former warrant officer, who was the chief instructor on the exercise, each face a single charge of negligently performing a duty.
They could face up to two years in prison and dismissal if convicted.
Both entered not guilty pleas during a hearing lasting less than half an hour.
The charges say they "performed a duty negligently, namely the duty to take reasonable care for the health and safety of candidates taking part in an exercise".
The Judge Advocate General, Jeff Blackett, said they faced a three-week trial on September 3 at a military court in Bulford, Wiltshire.
The trial by court-martial will be decided by a panel of five military personnel.