[PhantomGremlin]

Check the image of the P320 on Wikipedia.

https://en.wikipedia.org/wiki/SIG_Sauer_P320

Now look at the image of the Army handgun in this article. You can see a difference at the back of the slide, just about where a thumb safety should be. So it appears Sig added one. Wikipedia says (without attribution):

   The Modular Handgun System (MHS) or M17
   version of the P320 has an ambidextrous
   thumb safety.

[grzm]

I can see that my comment could be interpreted as questioning whether the P320 has a manual safety, which was not what I intended. I was asking for a reference that supports that Glock was dismissed for not having a manual safety. The fact that Sig apparently added one is circumstantial.

[Animats]

That makes sense. For most soldiers, a handgun is a backup weapon. If you're expecting trouble, you bring something bigger. To the military, handguns need to take minimum attention when not in use. Hence the requirement for an explicit safety.

[grzm]

When not in use a handgun will be in its holster. When it's needed, you'd arguably want less to think about, such as worrying about disengaging a manual safety.

They may well have been a requirement for a manual safety. If there were, I'm surprised that there hasn't been an explicit mention of this. There are rumors that it was down to Glock or Sig:

While a number of companies submitted guns, rumor has it that it came down to Glock and SIG.

https://www.americanrifleman.org/articles/2017/1/19/the-keef...

If Glock was disqualified for not having a manual safety, why wouldn't it have been eliminated earlier? Also, Glock did include in models submitted for Austrian trials (see comment by 'mrbill upthread https://news.ycombinator.com/item?id=13489074). For a contract as large as the US Army, I would imagine Glock would be willing to add a manual safety if it meant they'd get the contract.

Regardless, any of this is speculation unless there are definitive references out there that speak to why Sig was chosen over the other submissions.

[Animats]

Description of experienced firearms user shooting himself in the butt with a holstered firearm.[1] "I went to go get in the car and just heard a loud bang." The US Army reported in 2004 that about 10% of their casualties in Afghanistan were due to accidental weapons discharges.[2] The military wants guns that don't go off unexpectedly.

[1] http://concealednation.org/2016/02/when-bad-holsters-turn-wo...

[2] https://www.stripes.com/news/disturbing-trend-seen-in-neglig...

[grzm]

Wow. This all starts with me asking for a reference to support a comment by 'aplomb (https://news.ycombinator.com/item?id=13488853):

Glock was out of the running because lack of a "real" safety and their unwillingness to add one

Sure, there's some albeit circumstantial support for this claim. But so far, that's what it is, and definitely not conclusive.

(As an aside, general arguments comparing the safety of firearms with and without external safeties are all over the internet and not something I'm interested in re-litigating here. I'm interested in knowing whether this played a role in the Army's decision.)

The references you provide here don't do much to further this circumstantial support. [1] is explicitly an argument for better holsters, not safeties. It's not clear that a similar issue would arise in the military. I'm not aware of how frequently the Army uses concealed carry holsters, and poorly designed ones at that.

[2] doesn't break down what weapons were involved with the negligent discharges. Of the two that were described, one was a 9mm pistol, the other an M16 which was on safe. There's a possibility that the pistol was a Glock (or other pistol with no manual safety). The article is from 2004, and the Marine who was killed was part of 3rd Battalion, 6th Regiment, which later became part of Marine Special Operations Command (if I'm reading Wikipedia correctly), which approved the Glock 19 for use only in Marsoc in 2016. It's more likely that it was a Berreta M9, which features a manual safety, given that this is has been the standard issue 9mm pistol for the Marines. Neither of these examples show that safeties prevent negligent discharges.

Don't get me wrong. I'm fine with legitimate discussion about why the Army chose Sig over Glock. I'm by no means arguing that the decision was wrong. I think it's interesting to learn about what criteria come into play and how these decisions are made.