Documents released under the Freedom of Information Act indicate that the number of enlisted personnel leaving the military each year since US President George Bush launched his war on terror has increased from 8.7% in 2002 to 10.5% last year.
Enlisted losses - including people whose enlistments had expired - increased from 118,206 in 2002 to more than 137,465 last year, while officer losses have increased from 5619 in 2002 to more than 7500 last year.
The subset of those leaving before their term was up, for reasons ranging from disability to drug abuse, increased from 58,214 in 2002 to 60,406 last year among enlisted personnel and from 1011 in 2002 to 1280 for officers.
Lieutenant-Colonel Ellen Krenke, a Pentagon spokeswoman, said: "Service members leave the military for a variety of reasons."
"This is an all-volunteer military, which is dedicated to defending its country. We appreciate their service and respect their reasons for leaving the service."
Krenke said the military met and in some cases exceeded its retention goals this year.
None of the 1.4 million soldiers, sailors and marines on active duty today is allowed to simply quit the military, but they can be fired, or in certain cases receive special discharges.
The reasons for leaving the service differ in each branch, though general misconduct - a term which can mean anything from petty theft to brawling with colleagues - has consistently been the most common explanation.
Pentagon data going back 10 years shows that service losses last year were still below overall levels in the mid-90s, when the Defence Department struggled with both retention and recruiting.
"These days military parents are finding it very complicated to serve, because a lot of people are being deployed, many are being deployed multiple times"
Shelley MacDermid, director,
Military Family Research Institute
But in recent years, some categories reached 10-year highs.
Pregnancy and parenthood, for example, have steadily increased as a reason for personnel losses, especially in the army, where last year 4238 soldiers were discharged from the army for pregnancy and parenthood, up from 2862 in 2002 and 2565 in 1996.
This reflects what military officials say is a baby boom, especially at bases with high deployments.
Pregnancy used to mean an automatic discharge; these days, it is an option but not a requirement. Even so, increased numbers of service members are asking to get out because they have children.
Shelley MacDermid, director of the Military Family Research Institute at Purdue University in West Lafayette, Indiana, said:"These days military parents are finding it very complicated to serve, because a lot of people are being deployed, many are being deployed multiple times, and these deployments have proved to be unpredictable in length and frequency."
MacDermid said she had even heard of instances where soldiers "use pregnancy as a way to get out of a situation they do not like".
Drug use is also an increasing reason soldiers are being discharged from the army, up 40% since 2002; last year 1986 soldiers were discharged from the army for using marijuana, cocaine, ecstasy and other illegal drugs. By contrast, soldiers discharged for alcohol dropped from 251 in 2002 to 164 last year.
Rod Powers, a retired Air Force sergeant who writes for an advice column on the internet and has written books on the subject, said the drug use discharges probably reflected more sophisticated drug testing policies in all military branches.
US soldiers are struggling to keep
their weight down
"The military is getting smarter about drug testing, with better science and more random tests," he said. "I hear from a lot of young recruits thinking they can beat a urinalysis, but I tell them it's not so easy."
Powers has said the reduction in alcohol-related discharges is likely because most troops are not allowed to drink while they are deployed because they are posted in Muslim countries, and with longer and more frequent deployments there are simply fewer opportunities to imbibe.
Another issue that is prompting increased discharges is a failure to meet weight standards. The army, which has the most stringent weight standards of all the military branches, discharged more than 3285 soldiers last year because they were too heavy.
Beth Asch, who tracks armed forces staffing at the RAND Corporation, a non-partisan thinktank, said the army's weight problems may have been there all along.
"The big attrition due to weight is the army trying to make its recruiting mission by waiving the weight standards," she said. "The problem with doing that is those people tend to drop out."
The Marines and Air Force, by contrast, dropped standard weight tables and have used body fat measurements instead.
They have seen sharp declines in the numbers of troops being released due to weight problems.
The high profile and usually controversial discharges - such as conscientious objection and homosexuality - represent a small fraction of the total losses.
'Don't Ask, Don't Tell'
Only about 40 uniformed personnel received honorable discharges as conscientious objectors last year. The Pentagon did not release 2005 numbers of those released for homosexual conduct, but in 2004 just 653 people were discharged under the Don't Ask, Don't Tell policy. That was down from a 10-year high in 2001 of 1273.
Powers said he had heard from service members that commanders "aren't buying it when someone says they are a homosexual" and should be released from their obligation.
Service members released because of pregnancy or because they are disabled almost always receive honourable discharges, but those who are discharged for drug use or weight problems often end up with the black mark of a dishonourable or less than honourable discharge on their record.
Chris Lopez, a San Diego-based recruiter who helps place retiring military personnel in civilian jobs for the Lucas Group firm, said a negative discharge "is going to make it very difficult for some people to find work".
But he said honoruable discharges for things prompted by disability or dependency did not hinder career placement.