[msl]

Drum memory [1] and hard disks [2] have been used in nuclear tipped missiles, which are supposed to operate in an environment where EMPs are expected. Both types use magnetism for storing data.

[1] https://en.wikipedia.org/wiki/ASC-15 (Titan II)

[2] https://en.wikipedia.org/wiki/D-17B (Minuteman I) (note that the hard drive was used as RAM)