I believe the ability to have a Requiem for the dead of the two World Wars is unique to England & Wales. It is not mandatory, the remaining Sunday after Epiphany may be celebrated but it is a poignant day and the Holy Sacrifice of the Mass is the most fitting way of marking those who fell for our freedom. It also fits nicely with month of November and our remembering of the Holy Souls.
Of course this does not occur in the Novus Ordo Mass, whilst there will have been references to the Remembrance Sunday at most Masses in the New Rite, the ability for Requiem Mass is not there.
I am obliged to Canon Bernard Lordan for his continuing support for the Traditional Mass.