The US has been undertaking an irregular form of foreign aid, Sovereign Bond Guarantees, which entails guaranteeing some of the public debt of their allies, source here: https://www.cgdev.org/blog/whither-us-sovereign-bond-guarantee-program
The entire idea is that some states cannot access financing because they are not perceived as trustworthy, stable, or established enough. This creates a negative spiral, as high interest rates increase the probability of default. Guaranteeing the debt is bound to decrease the interest rate, making financing much easier and cheaper.
My question is: Has any other state done anything like this before? Who, when, where? Guarantees of private debt are common, but are there any other cases of state debt being guaranteed?
Is this an efficient form of foreign aid?