The idea that Christians cannot participate in war is a false one. The decision to join an army or not to join an army, to join a war or not to join a war, is always down to the individual. Draft or no draft, penalty or no penalty, the decision of whether or not to fight is always down to an individual. A christian has to make the decision based on his christian conscience.
The blunt facts of history show us that there are things worth fighting for. There are things worth more than another person's life. Even the Dubs hope for a war to save them - Armageddon. Therefore, some Christians, indeed, many, decide to join an army for a worthy cause and then wage the war as professionally, humanely, and justly as possible. There are just wars. Led by propoganda, or human frailty, we may indeed wind up with a situation where English Catholics kill German Catholics.
How can the Catholic church "wink" at this? Simple. The Catholic church does not attempt to gain the solid mind control over the individual that the WT does. The Church, once home of the Inquisition and the Pogrom, actually demurs to the individual conscience in this matter. Although in larger terms, it has come out against the dogma of a pre-emptive war. Anyway - the individual conscience is not the province of the Church. How to wage a just war is not a question open to bishops, rather, it is the province of Christian soldiers.
CZAR