When used in military service there was an external box like the CU-25, 26 or CU-32 that was referred to as a loading coil but it was the entire output tank for the transmitter in the LF band. They also used a trailing wire antenna that would be extended out the aircraft that had a lead weight attached to provide a long wire antenna for LF operations.
Benn told the stories by the old timers who were onboard aircraft such as the B-29 and later KB-29 and KB-50 tankers that sometimes they would extend the long wire antenna and forget to crank it back in and of all the damage that the lead weight would do to the houses in Ashiya and Yokota when landing.
Radio Boulevard has a great web site on the transmitter at:
https://www.radioblvd.com/art13.htmThink that has a section on operating on LF
RF