– Defense Technology International – The original stealth weapons, submarines may be second only to unmanned systems in the degree to which they have exploited new technology in the past two decades. Major advances have included air-independent propulsion (AIP) systems, increasing submerged endurance and mobility; automation, reducing crew size (and consequently, life-cycle costs) and improving habitability; electro-optical masts that can sweep the horizon with high-definition in seconds and drop out of sight; and new torpedoes and other weapons. On the near horizon is the the mating of SSKs with unmanned air and underwater vehicles (UUV).