Four U.S. Marines are presumed dead following yet another tragic incident involving Marine Corps aircraft on Tuesday. That crash was one of two incidents involving Marine Corps aircraft going down within just hours of each other.

The Marines were traveling over Southern California near the Mexican border when their CH-53 Super Stallion was lost on radar at approximately 2:35 p.m. local time. Thus far, very little information regarding the incident has been released by Marine Corps officials, though it is unusual for the branch to seem uncertain of the Marines fate even hours after the incident.

“The status of all four is presumed dead pending positive identification,” read a statement from the unit.

Once the status of the Marines have been confirmed, family notification procedures will be initiated and their identities will remain withheld for 24 hours as notification teams engage with the family.