Submarines can work at greater depths than are survivable or practical for human divers. A survivable ICBM would address this issue. Both these vehicles were armoured to make them more survivable in the battle environment. The Air Force responded by beginning research into survivable strategic missiles, starting the WS-199 program. Report P-2626 described a general architecture for a large-scale, distributed, survivable communications network. Hezbollah's small Katyushas rockets are somewhat man-portable and more survivable. Paul Baran and Donald Davies developed packet switching, a key part of "survivable communications networks". They flee, and Samson enters his car with painful but survivable injuries. Whether survivable or not, they are often accompanied by significant other injuries. A snorkel made a U-boat more survivable and losses to aircraft went down. The National Transportation Safety Board concluded that the accident was not survivable. Prior to this intervention cardiogenic shock was 100% not survivable. From the perspective of humanity, these can be subdivided into survivable risks and terminal risks. The network is designed to be highly survivable. This included development of strategic weapons systems that were more accurate, more survivable, or both.