Replay attacks and their associated risks in mobile tactical networks are analyzed and a cooperative joint detection scheme is evaluated. The scheme adopts a combination of duplicated frame detection and link likelihood verification to defend against both local and remote replays. A formal analytical framework is established employing realistic tactical radio models and network scenarios. The results obtained illustrate the network-wide risk of the attack and the effectiveness of the detection scheme. Though tactical networks employ link level encryption to ensure secure communications, packet replay attacks may be possible.