National technical means of verification (NTM) are monitoring techniques, such as satellite photography, used to verify adherence to international treaties. The phrase first appeared, but was not detailed, in the Strategic Arms Limitation Treaty (SALT) between the US and USSR. At first, the phrase reflected a concern that the "Soviet Union could be particularly disturbed by public recognition of this capability [satellite photography]...which it has veiled.". In modern usage, the term covers a variety of monitoring technologies, including others used at the time of SALT I. It continues to appear in subsequent arms control negotiations, which have a general theme called "trust but verify". Verification, in addition to information explicitly supplied from one side to the other, involves numerous technical intelligence disciplines. Measurement and Signature Intelligence (MASINT) techniques, many being especially obscure technical methods, are extremely important parts of verification. Outside of treaties, the techniques described here are critical in overall counterproliferation work. They can gather information on the states, with known or presumed nuclear weapons, that have not ratified (or are withdrawing from) the Nuclear Non-Proliferation Treaty (NPT): India, Israel, North Korea, and Pakistan. While the techniques here are focused primarily at missile and nuclear weapons limitation, the general principles hold for verification of treaties to counter the proliferation of chemical and biological warfare capabilities: "trust but verify". Imagery Intelligence Imagery intelligence (IMINT) taken by satellites (e.g., US CORONA, KH-5, etc.) covert high-altitude reconnaissance aircraft (e.g., Lockheed U-2) and drones/unmanned aerial vehicles (e.g., Global Hawk), and sensor-carrying aircraft allowed by treaty (e.g., OC-135B Open Skies), is a fundamental method of verification. Specific "protocols" spelling out the details of treaty implementation may require cooperation with IMINT, such as opening the doors of missile silos at agreed-to times, or making modifications to aircraft capable of nuclear weapons delivery, such that these aircraft can be identified in photographs. These methods provide an actual count of delivery vehicles. although they cannot look inside and count warheads or bombs. Interpretation involves art, science, and experience. For example, US intelligence used a discipline called "crateology" to recognize Soviet missiles and bombers, from the distinctive way the Soviets crated them for ocean shipment. Dino Brugioni gives an extensive account of imagery interpretation during the Cuban Missile Crisis in his book, Eyeball to Eyeball. The methodology he describes for counting missiles moving into Cuba, emplaced there, and later removed are direct parallels to the way in which