EXCELLENT CONDITION-OFFERS ACCEPTED? HSC-21 BLACKJACKS US NAVY CHIEF PETTY OFFICER / MESS CHALLENGE COIN Up for sale is a highly detailed HSC-21 “Blackjacks” U. Navy challenge coin featuring a Chief Petty Officer / Chiefs Mess theme. The coin has an impressive multi-layer, 3D design with black, silver, red, green and gold detailing. The front features the HSC-21 Blackjacks insignia along with SEAL Team Three imagery, playing-card/Blackjack elements, and additional military details. The reverse features a detailed U. Navy-themed design with the eagle, anchor and Chiefs imagery.