only by food supply. It is unlikely that any conceivable opponent of any nuclear power deploying ballistic missile submarines can locate and neutralize every ballistic missile submarine before it launches a retaliatory strike in the event of war. Therefore, to increase the percentage of nuclear forces surviving a first strike, a nation can simply increase SSBN deployment and the deployment of reliable communications links with SSBNs. Hardening or mobilizing land-based nuclear assets In addition, land-based ICBM silos can be hardened. No missile launch facility can really defend against a direct nuclear hit, but a sufficiently hardened silo could defend against a near miss, especially if the detonation is not from a multimegaton thermonuclear weapon. In addition, ICBMs can be placed on road or rail-mobile launchers (RT-23 Molodets, RT-2PM2 Topol-M, DF-31, Agni 5, Agni 6, MGM-134 Midgetman), which can then be moved around. As an enemy has nothing fixed at which to aim, that increases its survivability. Increasing alert state and readiness The effectiveness of a first strike is contingent upon the aggressor's ability to deplete its enemy's retaliatory capacity immediately to a level that would make a second strike impossible, mitigable, or strategically undesirable. Intelligence and early warning systems increase the probability that the enemy has the time to launch its own strike before its warmaking capacity has been significantly reduced, which renders a first strike pointless. Alert states such as DEFCON conditions, apart from serving a purpose in the internal management of a country's military, can have the effect of advising a potential aggressor that an escalation towards first strike has been detected and therefore that effective retaliatory strikes could be made in the event of an attack. Maintaining survivable C4ISTAR links Looking Glass, Nightwatch, and TACAMO are US airborne nuclear command posts and represent survivable communication links with US nuclear forces. In the event of significant political-military tensions between the nuclear powers, they would take to the skies and provide survivable communications in the event of enemy attack. They are capable of the full exercise of all available MAOs (Major Attack Options), as well as the full SIOP, in the event of a first strike or the destruction of the NCA. They can directly initiate launch of all American ICBMs via radio and satellite communication, signal SLBMs to launch and send bombers on their strike missions. In addition to those airborne assets, the US government has several command