I believe that the changes to the front were an attempt at modernisation and not a necessary repair job because there seems very little wear showing on the many photos just prior to the change.
If the windows were rotting it would be very surprising considering how similar windows all along the Esplanade have survived the elements. If they were not rotting then why replace them and change the single oriel window upstairs into two smaller plain windows?
The curved glass in the windows had not broken in storms, even the ones of 1924/25 when the seawall gave way. Newspaper reports say that some glass was broken in the doors so surely they would have mentioned if the windows had been damaged too?
The ‘cutting edge’ architectural style at that time was the International style, a plain form of Art Deco. They took the gable wall of the Drill Hall down to half way and rebuilt it it would appear. This is not the action of an organisation trying to save money. If the windows and stonework had needed replacing it would have been a lot cheaper to take the stonework down leaving the brickwork untouched; and replace the projecting bay windows with flat ones occupying the same openings.
The major work at the Ham to lay it out as a municipal style pleasure ground happened in 1929, the toilets were built at the same time. It is not unreasonable to suppose that these works prompted the Territorial Army to ‘upgrade’ the Drill hall in keeping with the new project.