I can answer this for Sweden.

While Sweden was not at war during ww2, it did mobilize to various degrees several times during the war - in November 1939, roughly 100 000 men were called into the II. Armékåren (2nd Army Corps) guarding the border with Finland against potential Soviet advances. This was 1,5% of the population. In early May 1940 there were 400 000 men in uniform, or 6,3% of the population. This was as close as Sweden ever got to a total mobilization. In August 1943 there were 300 000 men in uniform, or 4,7% of the population.

With a total mobilization, Sweden would have some 400 000 men (1940) to 600 000 men (1943) under arms, plus 100 000 men in the home guard.

The Swedish army paid its conscripts, but the pay was low. Soldiers of the Stockholm garrison, paricularly the guards cavalry units prostituing themselves (almost excusively to older gay men in the upper class quarters the guards barracks were located in) were a problem that was declared "eradicated" several times during the early 20th century.

A conscript soldier recieved 1:- (1 SEK) a day in 1940, with conscript NCOs and officers getting sligtly more. However, an unskilled labourer could expect to earn 10:- a day in the civilian market. Even if the soldier had food, clothes, housing and travel for leave paid, it was still very little money.

Before 1940, this had rarely been a big problem, as initial conscription happened at the age of 19 or 20, and most young men had little commitments, duties and costs, often still living at home. However, when mobilizing, there were a lot of family fathers and primary income makers that were removed from their homes and families - and with them their income. Normal repeat training for conscripts were usually a single month, but with the various levels of mobilization during the war, this could last up to 6 months, which caused considerable hardship for the families involved.

By law the conscript's employment and position was protected - employers were barred from firing or disfavouring men for doing their compulsory military service, but the problem during the actual service remained.

Thus in 1940, extra pay for family fathers were introduced for men with families - from 1:75 to 2:20 per day depending on wether the wife was able to work and the number of children - increasing the max potential income of a conscript to 3:20 per day, or 32% of what an unskilled labourer could earn per day.

A rent subsidy (which could also be applied to mortgages for houses and apartments) was also introduced, but not specified to a certain amount - only that if the pay and extra family pay was not enough to cover rent, a further amount could be applied for, tried by a comittee and then approved if necessary. It was also suggested that a rent reduction with 20% be enforced by law during conscription service, but the implementation was considered a bit too cumbersome, so the rent subsidy was introduced instead.

I will answer your question from the US perspective with a question of my own. In 1941-1942 the US passed and began implementing the Emergency Price Control Act, which included some powers around national rent control. I think the way it operated was that it would set up Federal consequences if states and municipalities didn't address housing problems locally. Most large cities (populations over 100,000) throughout the US ended up under federal rent control before the end of the war.

The US also invested a lot in building new housing stock and subsidizing various parts of the housing market. Federal loans for home ownership and construction of public housing began during this time.

Thirdly, "rent parties" is definitely going to be at least part of the answer, along with eviction blockades and other radical actions to keep families housed, whether or not they could pay rents. There were rent parties in Harlem long before WWII.

I would also like to learn more about other countries besides the US and Sweden, and also much more about the US policy around national rent control.