I Found this that could have an alternate senario for missle jackets:
A "salted" nuclear weapon is reminiscent of fission-fusion-fission weapons, but instead of a fissionable jacket around the secondary stage fusion
fuel, a non-fissionable blanket of a specially chosen salting isotope is used (cobalt-59 in the case of the cobalt bomb). This blanket captures the
escaping fusion neutrons to breed a radioactive isotope that maximizes the fallout hazard from the weapon rather than generating additional explosive
force (and dangerous fission fallout) from fast fission of U-238.
Variable fallout effects can be obtained by using different salting isotopes. Gold has been proposed for short-term fallout (days), tantalum and zinc
for fallout of intermediate duration (months), and cobalt for long term contamination (years). To be useful for salting, the parent isotopes must be
abundant in the natural element, and the neutron-bred radioactive product must be a strong emitter of penetrating gamma rays.
The rest
of the article,,,,,
It could be there were cobalt 59 or even cobalt 60 jackets on that battleship.
Bode