Whatever the weather, the work of the Household Cavalry Mounted Regiment providing the Queen's Life Guard must go on.
So, while the UK swelters in soaring temperatures – predicted to reach 40°C in London on Tuesday – personnel are having to come up with imaginative ways to keep their hot horses cool.
Forces News has been to Horse Guards Parade to see how they are managing in the heat – and find out what special care the military horses are getting to help them stay fit and healthy.
For the horses providing the Queen's Life Guard at Horse Guards Parade, standing in a box for an hour in a heatwave can test their patience.
"They are very stressy, I would say," said Trooper Brandon Richard, Household Cavalry.
"I'm 80 kilos, add another 30 kilos of kit on top of that horse, you're looking at over 100 kilos on top of that horse, as well as all the heat.
"So yeah, they are very stressy at the minute."
Intense sweating in the heat can have health implications too if the animals are not given the right food, drink and treatment.
Trooper Maxwell Nicholls, Household Cavalry, said: "When we come back in we'll sponge them down usually and get rid of some of the sweat that they've got on them, just get rid of it so it doesn't sit on them and go all crispy and horrible, and make them a bit more comfortable in the stall.
"Usually we will give them a recovery mash as soon as they get in, which will, sort of, replenish everything they need, and make sure they've got water and maybe some snacks as well, just to get their energy up."
The recovery mash contains electrolytes to replace minerals that are lost through sweating.
These horses are chosen for their calm nature – even without the added pressure of the heat, they have to put up with tourists and London traffic.
Keeping the horses in the shade is also key during the hot weather and, in the stables at Horse Guards, there is plenty of that.
Apple bobbing, too, in buckets or troughs filled with cold water, has become a favourite pastime for the horses trying to keep their cool.