The pocket guide, launched earlier this week by the Ministry of Defence (MoD) and the charity Samaritans, suggests ways of offering support and signposts sources of help.
All military personnel and reservists, of which there are around 200,000, will receive either a hard copy or a digital version of the guide, which is the first of its kind given to soldiers.
It advocates “looking after your mates” and covers the behaviour that might indicate someone is not coping with a mental health problem, as well as when to intervene, support and report those who may be struggling.
Warning signs listed include a loss of personal discipline, drinking alone and appearing “not quite there”, as well as negative statements such as, “It’s like everything is against me”, The Telegraph reports.
The military suicide rate, at eight deaths per 100,000 people in 2017, is lower than that among the general population, which was 18 per 100,000 in 2016.
Suicidal thoughts and behaviours may be triggered by events such as losing custody of a child or the recent loss of a friend, the booklet says.
Defence secretary Gavin Williamson said: “I want to ensure no one in our military suffers in silence. It is vital that service personnel know where to turn to in times of crisis and this guide will raise awareness of the support available.
“By helping our people to spot the early signs that someone may be struggling, we give them the best chance of a full recovery.”
The new booklet is part of a £3.5m series of initiatives by the MoD and Samaritans designed to offer training and support to serving personnel, veterans and their families with mental health problems.
The MoD is investing £220m over the next ten years to improve mental health services for those in the armed forces.
In February a 24-hour mental health helpline was set up for serving personnel and their families, funded by the MoD and run by the charity Combat Stress.