Also, from a gameplay standpoint, consider how much of allied strategy over the years focuses on getting Western Units towards the center to prop up Moscow. The assumption thus far has been that when these units are on Russian territory they represent basically the leasing of equipment. Since it makes no sense otherwise, historically anyway, to have western armies roaming around in the Soviet union. In reality we spent millions in the form of aid and equipment, but the forces amassed there were still under Russian command. It makes more sense if the W. Allies could just give Russia money as a loan with a built in cost, rather than flying or shucking units onto their land.
Likewise consider all the gold and wealth that the UK transferred to secure locations in North America, the largest such transfer in history, known as “Operation Fish”, ensuring that the money not fall into German hands. Or the economic direct cooperation between the various Axis powers.
By incorporating an official mechanic for “Lending” into the game, with balanced rules, we can avoid the alternative (rather weird) phenomenon of ally nations propping each other up with co-located units. Japanese fighters to Europe, or western Fighters to Moscow being the prime example. Here you have a simple way to provide direct aid (at a cost), which I think will encourage less multinational unit (space hogs) on defense, at least in the areas of the map were mass crowding occurs. Instead you’d have more direct aid for purchase in the form of Loans to the ally.
Think about how it could work. In this case USA could use their starting income to assist Russia or UK directly at the 2:1 cost. Likewise Japan or Germany could aid whichever power is weakening directly instead of with mass fighter spams and air shifting like we tend to see now. Loans would provide a way to get around this, but only at a fairly substantial cost in terms of total ipcs.
*Another option for this rule, which you can use for game balance (to prevent overpowered loans) is to cap the total loan amount at no more than half the lender Nation’s total reserves. So in this case if a nation had 40 ipcs total, they could use up to half of this (20 ipcs) on loans to any ally. This caps the total number of units that could be introduced using this mechanic in any given round, if one wanted to restrict the overall impact while still retaining the essential flavor of the rule. Whether a cap is advisable or not depends on which board you are playing, and how much total income is in circulation (if you have lots of NOs or other income HRs in play you may wish to consider the cap.) Even with a cap at half the reserve though, and even at the 2:1 ratio, the ability to lend can provide powerful strategic opportunities for both sides at various points in the game.
One interesting question is when exactly (within the Players turn) should the Loan phase occur?
If all Loans are made after “collect income” as the final phase, it would force players to allot their money in advance, and allow for the evacuation of wealth from a Capital if desired. If the Loan phase came right after collect income, I can see many positives on potential purchasing strategy.