Why giant ELF submarine antennas can still be defended

Are extremely low frequency submarine-communication antennas vulnerable because they are so large?

They remain vulnerable, but remote inland siting and strong defences can make an attack a major operation; a nuclear ballistic missile is raised as the extreme alternative.

The size of an ELF installation makes it vulnerable in principle. Its location is flexible, so it can be placed in a remote interior region behind substantial defences. Reaching it could require a large conventional strike, with a nuclear-armed ballistic missile raised as the extreme alternative. A suggested American location is corrected because the facility being recalled uses very low frequency communications, not extremely low frequency. The distinction matters when comparing the installations.