WEST POINT, N.Y. — An annual freshman pillow fight at the U.S. Military Academy turned bloody this year when cadets swung pillowcases packed with hard objects, injuring 30 cadets, according to a newspaper report Saturday.

Two dozen cadets suffered concussions in the Aug. 20 bedding melee, though all have since returned to duty, West Point spokesman Lt. Col. Christopher Kasker told The New York Times for a story published Saturday. While photos and video of the episode have circulated online for some time, West Point officials didn’t confirm what had happened until Thursday, the newspaper said. The phone rang unanswered Saturday at the academy’s press office.

First-year students, known as “plebes,” organize the pillow fight as a way to build camaraderie after a grueling summer of training for the rigors of West Point, Kasker told the Times. The elite academy has trained generations of Army leaders and counts U.S. Presidents Ulysses S. Grant and Dwight D. Eisenhower among its graduates.

“West Point applauds the cadets’ desire to build esprit and regrets the injuries,” Kasker said, adding that the school is investigating what happened. No cadets have been punished thus far.

He said upperclassmen overseeing the fight required cadets to wear helmets. However, online video showed many bare heads.

Some cadets swung pillowcases believed to have been packed with their helmets, the Times said.

There are no plans to end the annual pillow showdown.