These camps all shared the same unique function, among other activities.

Camp Alva, Oklahoma,
Camp Como, Mississippi
Camp Indianola, Nebraska
Camp Siebert, Alabama
Camp Hood, Texas
Camp Crowder, Missouri
Holabird Signal Depot, Maryland
Halloran General Hospital, New York
Pine Bluff Arsenal, Arkansas
Fort Riley, Kansas
Fort Dix, New Jersey

What was it?

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Best Regards,
JW