Sexual harassment in the military
Definitions: Sexual harassment is unwanted sexual behaviour experienced as threatening or otherwise upsetting. Definitions in use by state armed forces include:

Australian Defence Forces: Unwanted sexual advances or sexual requests towards to another person
British Army: Unwanted sexually based conduct or other conduct affecting the dignity of women and men at work.
Canadian Armed Forces: Improper conduct directed at and offensive to others, which the perpetrator ought reasonably know would be so.
United States Armed Forces: Unwanted sexual advances and other behaviour of a sexual nature.

Behaviour: Sexual harassment in the military includes a broad spectrum of behaviour.
Undirected behaviours are those not personally targeted but which affect the working environment, such as sexist and sexual jokes and the prominent display of pornographic material.
Directed behaviours target one or more individuals, such as hazing rituals, unwanted sexual advances, and sexual assault.
Research in Canada has found that a military culture of undirected sexual harassment increases the risk of directed sexual harassment and assault.

Case examples: A woman in the British army told researchers in 2006:A friend was out on an exercise when a group of men ducked her head in a bucket of water and each time she came up for breath she had to repeat "I am useless and I am a female". She told the story and said it was a joke but I could see she was upset.The Deschamps Review of 2015 found pervasive demeaning attitudes to women in the Canadian armed forces:Interviewees reported regularly being told of orders to "stop being pussies" and to "leave your purses at home" [...] The use of the word "cunt", for example, is commonplace, and rape jokes are tolerated. [...] A commonly held attitude is that, rather than be a soldier, a sailor or an aviator, a woman will be labeled an "ice princess", a "bitch", or a "slut". Another saying is that women enter the CAF "to find a man, to leave a man, or to become a man".A woman in the French army was raped by her commanding officer:It was months before I could pronounce the word "rape"... I blamed myself. I said: "We are trained in hand to hand combat. Why didn't I stop him?" But when that happens you are terrorised.Many incidents of sexual harassment and assault in the US armed forces have been documented. For example:
When a woman in the US army attended a sexual harassment awareness training, the senior officer teaching the class asked participants whether they would hit on "a naked, drunk girl on the bench outside your barracks", adding, "you're not supposed to but I probably would".
US Senator Martha McSally, formerly of the US Air Force and the first female pilot to fly combat operations, testified to a Senate meeting that she was raped by a superior officer. McSally explained that she never reported the incident for lack of trust in the military justice system. She added that she blamed herself, and that although she had thought herself strong, she felt powerless.

The US Navy Tailhook Association scandal exposed multiple acts of sexual violence during the organisation's annual convention of aviators in Las Vegas. Lieutenant Paula Puopolo (then Coughlin) blew the whistle on a run-the-gauntlet ritual, in which male officers lined the third-floor corridor of the convention hotel to harass and assault women passing through. In 1991, the men sexually assaulted 83 women, including Puopolo, and seven men. As reported in the Wall Street Journal:Puopolo says up to 200 disheveled airmen set upon her. She was fondled and passed along from one groping, pinching set of hands to another before being dropped to the ground. At breakfast, Puopolo reported the incident to [Rear Admiral] Snyder, himself a former president of the association. "He said that's what you get when you go down a hallway full of drunken aviators," she recalls.

Principal targets: 

Female personnel: While some male personnel are sexually harassed, women are much more likely to be targeted.
Younger women and girls face a greater risk, according to American, British, Canadian, and French research. For example, girls aged under 18 in the British armed forces were ten times as likely as adult female personnel to be the victim of a sexual offence in 2021.

Intimate partners: In 2022, research in the UK armed forces found that experience of intimate partner violence (IPV), a category that includes sexual abuse, was three times more prevalent among partners of military personnel than among partners of civilians. 10% of male and 7% of female personnel told the researchers they had abused their partner in the previous 12 months. The study found that physical and sexual abuse of partners was particularly common where personnel had traumatic experiences of war.
In the US armed forces, estimates of the sexual abuse of military partners indicate a similarly high rate of annual incidence, ranging from 12% to 40%.

Child cadets: Cadet forces, common worldwide, are military youth organisations in communities and schools. Some evidence from the UK, where hundreds of complaints of the sexual abuse of cadets have been recorded since 2012, and from Canada, where one in ten complaints of sexual assault in the military are from the cadet organisations, indicate that these institutions are susceptible to a culture of sexual harassment.

Detainees: Individuals detained by militaries are particularly vulnerable to sexual harassment. During the Iraq War, for example, personnel of the U.S. Army and Central Intelligence Agency (CIA) committed multiple human rights violations against detainees in Abu Ghraib prison, including rape, sodomy, and other forms of sexual abuse. Similarly, two Iraqi men detained on a Coalition warship at the start of the war were made to strip naked and were sexually humiliated.

Prevalence: While prevalence varies by country, military branch, and other factors, official statistics and peer-reviewed research from Canada, France, the UK, and the US indicate that between a quarter and a third of military women in these countries are sexually harassed at work at least once each year.
Military training settings are characterised by a particularly high level of sexual harassment and assault relative to both the civilian population and other military settings. 
Research further shows an increase in perpetration during and after deployment on military operations.
Studies of sexual harassment have found that it is markedly more common in military than civilian settings For example, between 2015 and 2020, girls aged 16 or 17 in the British armed forces were twice as likely as their same-age civilian peers to report rape or other sexual assault.

Risk factors: Several reasons for a high prevalence of sexual harassment in the military have been suggested.
A Canadian study has found that key risk factors associated with military settings are the typically young age of personnel, the isolated locations of bases, the minority status of women, and the disproportionate number of men in senior positions.
An emphasis in military organisations on conformity, obedience, and hierarchical power relations, combine to increase the risk, particularly to personnel of low rank, who are less able than others to resist inappropriate expectations made of them. 
Traditionally masculine values and behaviours that are rewarded and reinforced in military settings are also thought to play a role. 
In the UK, the 2019 Wigston Review into inappropriate sexual behaviours in the armed forces reported that several military factors contributed to risk: "tight-knit units that perceive themselves as 'elite'; masculine cultures with low gender diversity; rank gradients; age gradients; weak or absent controls, especially after extensive operational periods; and alcohol."

Effects: Women affected by sexual harassment are more likely than other women to suffer stress-related mental illness afterwards.
Research in the US found that when sexual abuse of female military personnel was psychiatrically traumatic, the odds of suffering from post-traumatic stress disorder (PTSD) after deployment on operations increased by a factor of nine, and the odds of suicide more than doubled.
Research in the US has found that personnel affected by sexual harassment are somewhat less likely to develop depression or PTSD if a formal report leads to effective action to address the issue.

Institutional responses: The military leadership in some countries has begun to acknowledge a culture of sexual misconduct among personnel. For example:

The British armed forces co-commissioned their first formal study of the problem in 2006. In 2016, the head of the British army noted that soldier culture remained "overly sexualised" and committed to reducing the extent of sexual misconduct.
In 2016, after a major study uncovered widespread sexual harassment and assault in the Canadian armed forces, General Jonathan Vance, Chief of the Defence Staff, acknowledged: "Harmful sexual behaviour is a real problem in our institution."
The US established the Sexual Assault Prevention and Response Office in 2005, which reports annually. In 2019, Secretary of Defense Lloyd Austin remarked nonetheless that prevention efforts remained "far short of what is required to make lasting change".
Since the number of official complaints represents only a fraction of sexual harassment incidence, armed forces committed to reducing prevalence produce periodic estimates of its true extent by means of anonymised surveys.
Other prevention initiatives, varying by country, include bystander and diversity training, and helplines. Despite these steps, official statistics in Canada, the UK, and the US over the last decade show high and increasing rates of harassment.

Barriers to redress: Military personnel are frequently reluctant to report incidents of sexual misconduct:

An official report of the Australian Defence Force concluded that women affected by harassment were less likely to make a complaint because they do not expect a serious response.
Leila Minano, the co-author of a book documenting sexual abuse in the French armed forces, has commented that women are systematically discouraged from complaining, and often moved out of their unit if they do.