Thanks, all, for the considered posts in response to my query. All of this is quite useful and reminds me of a passage from Orwell's 'Homage to Catalonia' I read over the weekend and worth sharing:

'Wherever the lines were within hailing distance of one another there was always a good deal of shouting from trench to trench. From ourselves: "Fascistas -- maricones!" From the Fascists: "Viva Espana! Viva Franco!" ... On the Government side, in the party militias, the shouting of propaganda to undermine the enemy morale had been developed into a regular technique. In every suitable position men, usually machine-gunners, were told off for shouting duty and provided with megaphones. ... Of course such a proceeding does not fit in with the English conception of war."