Hard to imagine doing more than one pushup at a time.
I sentence you to 5 cream pies in the face.
The army scores you based on age and gender. A score of 60 is passing, you get two minutes. I for example and a 22 year old male and thus have to do 40 push ups in two minutes.
How many push ups are required for military people? It depends on your age and the branch of service you’re in.
A Navy Seal trainee, for example, is supposed to do something like 42 pushups in 2 minutes - minimum. They’d rather see 100 in the two-minute time period.
The requirement is lower for most other military folks. Push-ups are just part of the test, with sit ups and a run making up the remainder. The total score is the important thing. That’s the exercise part and, for many, the easy part. They also weigh in and it is a “good thing” to be under the weight limit for their height.
What they tell us now in the Air Force (we are in the process of revising the fitness standards) is that when you do the pushup, your elbows should “break 90”. That is to say, a correct pushup has your forearms parallel to the ground, but just short of that doesn’t count. So we are encouraged to go just past 90 degrees, to make sure we get it. But yeah, the chin touching the ground or not never comes up for us.
As far as head up or head down, seems to depend on who’s coaching. In Basic, the TI’s told us the only thing we’d see with our faces down was the ground before we hit it. Now that I’m in the Operational Air Force™, they tell us to keep our heads down so we don’t strain our necks/backs while doing the pushups.
And the situps/crunches thing is funny. We do crunches at PT in our squadron, as in, knees up, head off the ground, hands behind the neck, touch your knees with your elbows. When we take the PT test, we do crunches, as in have your feet anchored to the ground (with a bar or with a wingman), hands on your chest, and sit up so your elbows touch your thighs. Two entirely different workouts. 
ETA: Oh, and for the new fitness standards, a male in his 20’s (yo) would be required to hit at least 36 pushups and 45 situps in a minute each with a waist of 38" or less, plus a run time of I don’t remember how long. If you meet the minimums in each category, you’ll end up with a score that still won’t pass you, so you have to actually excel at something (my pushups and situps are marginal, but I am a pretty decent distance runner)
I meant throughout basic, aside from the tests. Are they constantly making you get down and do 20?
Not really from what I understand. I did plenty of push ups when I went through in 2006, but things seem to have changed a lot even in the last 4 years.
In general when I was going through BCT when you where made to do push ups you did them until you couldn’t do them anymore, whether that was 12 or 70.
I’m a little confused by the usage of ‘90º’ by some people. Do you actually have your hands spread out far enough that when your upper arms are parallel to the ground your elbows form right angles, or do you keep your hands further in and only go down until the elbows form a 90º angle?
I’ve always done it with my hands at shoulder width apart - so that the upper arms are parallel to each other at the top, and to the ground at the bottom, but this yields a much shallower angle at the elbow.
I’m a little confused, by definition, wouldn’t your elbows be at 90º (Hah! I copy pasted your º!) once your upper arms were parallel, since the lower arms are supporting your weight and presumably going straight up and down?
The only exceptions I can think of are if you have your arms way too far out, or if you have your hands inside your shoulderspan, meaning you’d break 90º before your arms went parallel to the ground.
No, with your upper arms parallel your elbows would only be at 90º if your hands are in the right position for it, which is well outside your shoulders (indeed, they must be exactly as far apart as your shoulders plus your upper arms). Your upper arm can be parallel to the ground with your arms outstretched (180º elbow bend) or with the hands fully inside (0º elbow bend, or near enough). Granted, you can’t support yourself that well in those situations, but there’s a good range in between the two that works.
Your elbows could also bend at 90º in other hand positions too, of course, hence my confusion.
Another type, and harder, push-up has the fingers of each hand forming a triangle, the thumbs forming the base. The lower arms, of course, are not parallel, but also form a triangle with the body. This exercise uses the triceps more.l
In the Air Force, we call those “Diamond Pushups”
I’m pretty sure they were invented to punish possible heretics during the Inquisition, along with Lunges.
Heh, when I was in JROTC, we went to Summer Leadership School, where the ROTC cadets leading PT could be heard to (often) say “YOU CAN’T AFFORD DIAMONDS THAT BIG!!”
I’ve just realized that there could be another arm motion involved as well; instead of splaying the elbows out to the side, they could remain in line with the body; in that case the hands can be right at shoulder width and a 90º angle can be formed. I’ve never really thought of doing them that way. Is that the technique you’re thinking of, raguleader?
Yeah, but it’s been One Of Those Days™ for me, and I couldn’t put all the thoughts in my head together to just say that.
The “diamond pushup” is a variation of that, but the diamond is easier.
That’s the style we do for our test. Hands directly under your shoulders/armpits and your arms bend along your body, not out. They suck and I hate them as I have no upper body strength to speak of.
Feet together…body held rigid and straight…elbows at 90 deg. to the body.
The tip of the nose touches the ground.
Another “tip of the nose,” pussy. 
I love my jarhead friends, especially when they are buying. It takes only a couple muttered syllables to create both another round and another demonstration of physical prowess that many appreciate but which I take as a drinking break.