At my fittest, which I'm certainly not now, I still would not have been able to complete the Infantry Combat Fitness Test, nor the regular CFT carrying Infantry or RAC weight. I know very few women that could - and most of those are heavier built or 'overweight' because of the muscle tone and body shape.
I've known women that could piss on the men at running, but it's not about running. Running (in shorts and T shirts wearing trainers) is of no use on the battlefield. You have to be able to wear a helmet, carry a rifle, wear boots and have up to 32Kg on your back and then trog for 8 miles in less than 2 hours. The Inf test is longer and faster.
The weight by you carry is trade specific, not sex, so women compete equally with the men in the same job as them.
Neither is it all about the battlefield.
Imagine sitting in an OP (observation point). You could be there for a number of days. You have dug a shell scrape to a depth of about 4 inches and are either inside a bivvy bag (like a gortex sleeping bag) or have a waterproof camouflage cover pegged over you.
You lie there, unmoving for 24/48/72 hours. You have your binoculars trained on a certain point, and cannot miss a minute of what is going on. You can't have a crap because you can't move. You eat cold boil in the bag rations because you can't cook.
You need a pee. Men stay in position, stick their penis into an empty coke bottle and relieve themselves whilst still in position, still watching, still holding the binos. You can't wet youself - for one if you are in a bivvy bag the urine will stay inside sloshing around you, for two it will alert animals to your presence that could give you away.
That one simple thing is harder for women. It has nothing to do with strength, or stamina or the will to do it. It's a design fault
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I could come up with a number of other scenarios, real ones, ones I have come across myself and ones I have had to overcome myself.
It's not all about the fitness, or the strength, or the bravery/gallantry, or the hearts and minds. It's the whole package and until we/they overcome every last issue then it's academic. Sure there are women that could do it (btw the standards have changed a lot since Kelly Holmes day), but they are very few and far between.