My understanding of the purpose of war binds is to suppress wages and private consumption and promote war production. It usually involves a lot of jingoistic propaganda, I guess because their attractiveness as an investment isn't able to stand on its own.

War bonds suppressing consumption to fund production is part of the story, but a deeper issue is that governments use bonds alongside inflation and financial repression to quietly wipe away debt rather than default outright. They looked at over three centuries of US and UK data and found that investors in government bonds lost about 14% in real terms during the first four years of major wars, and bonds underperformed stocks by roughly 23% over that same period. Inflation ran about 20% during these periods and policies like interest rate caps and central bank bond purchases pushed yields below market rates. So, the propaganda you mention does serve to keep people buying a depreciating asset. And the same pattern showed up during COVID-19, when bonds delivered large negative real returns, which supports the idea that this is a recurring feature of massive fiscal crises rather than something unique to wars.