A traditional pillow fight intended to blow off steam and mark the end of training at the US military academy West Point in New York turned bloody this year when some cadets stuffed pillowcases with hard objects.

West Point only confirmed on Thursday that 30 cadets had been injured in the August 20 pillow fight – 24 of whom had suffered from concussion.

“West Point applauds the cadets’ desire to build esprit and regrets the injuries to our cadets,” Lt. Colonel Christopher Kasker, spokesman for the academy, told The New York Times. “We are conducting appropriate investigations into the causes of the injuries.”

Colonel Kasker said the annual fight is generally organized by first-year students to build camaraderie and prepare them for the second year. Upperclassmen are supposed to take measures to prevent injuries, such as requiring cadets to wear helmets.

The fight turned violent when some cadets packed pillowcases with hard objects, thought to be helmets, causing split lips, a broken bone and dislocated shoulders while knocking other cadets unconscious, according to NYT.

Reports of problems with the fight first began circulating on social media the same night it occurred, including a video of the pillow fight:

A picture of a bloody cadet:

Most pillow fights? Harmless Pillow fight at West Point? Vicious #bloodbuildscharacterpic.twitter.com/2pIJC2YfO5 — Bradley Baker (@bradleypbaker) August 21, 2015

Followed by bloody pillowcases:

Dozens cadets at West Point were injured after bludgeoning each other in a pillow fight http://t.co/Ac7VxC0h5ipic.twitter.com/geWWn7MGcZ — Jim Dalrymple II (@JimDalrympleII) September 5, 2015

And emergency vehicles:

Only at West Point does a pillow fight put 13 kids in the hospital pic.twitter.com/PXDnRwz5fW — Matthew Brooks (@brooksmatthew1) August 21, 2015

Col. Kasker told NYT that no cadets have been punished and the academy has no plans to end the pillow fight.

West Point is the oldest service academy in the US, established in 1802, educating and commissioning an illustrious list of officers including recent alumni such as David Petraeus, former director of the CIA, Martin Dempsey, chairman of the Joint Chiefs of Staff, and retired Army General Stanley McChrystal.