The heat has slowed the events at Camp Manassas — most of the reenactors are sitting under the shade, women fan themselves. The heat today is fitting for the event the reenactors are commemorating, the sesquicentennial of the Battle of Bull Run.

“On that day 150 years ago it was just as hot maybe even hotter,” said David Kinkaid, a reenactor from New York City who wears the uniform of the 166th Pennsylvania, an Irish regiment composed of men from Philadelphia and Pittsburgh.(For more on the 1861 weather, see this post by the Capital Weather Gang.)

(Today, thankfully, there is a soft breeze which makes things slightly more tolerable.)

Gen. Irvin McDowell, commander of Federal forces at Bull Run, announced reveille at 2 a.m. to get to action before the hottest part of the day. That plan fell apart after his forces arrived three hours late and ended up fighting well through the hottest part of the day

At Sudley Ford men of the Second Rhode Island Infantry broke ranks in the middle of action to drink from the stream.

In the 69th New York, an Irish regiment, the soldiers peeled from their coats and fought bare-chested.

Kinkaid recited a ditty about the 69th:

The day will be remembered by America’s noble sons.

If it hadn’t a been for the Irishmen what would our Union have done

It was hand to hand we fought ‘em, all in the broiling sun

Stripped to the pants we did advance at the Battle of Bull Run

Dehydration was always a concern — an Army needs water more than ammunition. If men were too thirsty they might not be able to fire their muskets. Powder and rounds came in paper sacks that soldiers tore open with their teeth. If they were too parched the paper and powder would stick in their mouths and they could not spit them out. Sometimes regiments were removed from action for lack of water.

“Most people think it’s complete lunacy that they wore wool uniforms,” Kinkaid said. But in the heat of battle, soldiers’garb may have been a benefit.

Kinkaid’s blue Union coat is from the 19th century and it is so thick you cannot see the weave patterns. Because it doesn’t let air in and is water resistant it makes an effective insulator. When men sweat in the uniform it traps in the sweat and acts as a cooler. He recalled once removing his coat after a battle reenactment and heating up considerably. He put it back on to cool off.

But, one must still remember to drink lots of water.

The Post’s Timothy R. Smith will be blogging all day from the events in Manassas honoring the 150th anniversary of the Battle of Bull Run.