Tracking submarines under or near ice is difficult, because ice constantly shifts, crackles and groans loudly enough to mask the subtle sounds of a submarine. If it breaks up completely, as its two smaller siblings (Larsens A and B) have done over the past 20 years, that ice on shore could flow much more easily into the ocean. Less than two months later, Russia conducted a similar test in the White Sea, north of Archangel. America, Britain, China, France and Russia all have nuclear-powered submarines on permanent or near permanent patrol, capable of launching nuclear missiles; India has one such submarine, too, and Israel is believed to have nuclear missiles on conventionally powered submarines. If a submarine is detected by such a system, it can then be trailed by another submarine, or some new form of drone. An officer on the ballistic-missile submarine USS George Washington sent a message to President Dwight Eisenhower: “POLARIS-FROM OUT OF THE DEEP TO TARGET.