When Orwell says “the Government side,” he means the anti-Franco forces, nominally fighting for the overthrown center-left government albeit also engaged in a revolution.
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. Generally they shouted a set-piece, full of revolutionary sentiments which explained to the Fascist soldiers that they were merely the hirelings of international capitalism, that they were fighting against their own class, etc., etc., and urged them to come over to our side. This was repeated over and over by relays of men; sometimes it continued almost the whole night. There is very little doubt that it had its effect; everyone agreed that the trickle of Fascist deserters was partly caused by it. If one comes to think of it, when some poor devil of a sentry- very likely a Socialist or Anarchist trade union member who has been conscripted against his will- is freezing at his post, the slogan “Don’t fight against your own class!” ringing again and again through the darkness is bound to make an impression on him. It might make just the difference between deserting and not deserting. Of course such a proceeding does not fit in with the English conception of war. I admit I was amazed and scandalized when I first saw it done. The idea of trying to convert your enemy instead of shooting him! I now think that from any point of view it was a legitimate manoeuvre.
Homage to Catalonia, p42