Further to my last:
If I look at the stern of this one container ship and consider only those containers flush with the stern in the top row and the stepped back upper row I find
15x Reefer Containers on the top of the central block
2x Reefer Containers flanking the central block
11x Reefer Containers surmounting the central block with an additional 6x dry boxes flanking them.
Considering just the reefers for the moment, and replacing them with the Mk70 PDS from Lockheed Martin, with 4 strike length cells each,
the those 28 Mk70s could carry 112 cells. An Arleigh Burke only mounts 90 to 96 cells.
15x 4x ESSM Quad packs = 240 ESSM SAMs
11x 4x ASROC = 44x Mk 54 lightweight torpedoes
2x 4x Tomahawk MST = 8x Tomahawk
If you add the 6 dry box equivalents with an additional 24 cells then you might start adding NSMs.
Or perhaps you want to mount 3 or 4 Rheinmetall 35mm Millenium AD guns.
....
None of that would materially impact the cargo vessel's load carrying capacity and it would be a lot more effective that adding robotugs with four TEU-40 spots to the fleet.