Is it structured to fend off the asset-eroding potential of triggers such as so-called Black Swan events, Black Monday-level market implosions, interest and inflation rate swings, war or an oil supply disruption?
The liquidity and trading in those older issues is so tiny that it doesn't give much guidance as to the potential cost for the government of borrowing substantial sums at what are known as ultra long maturities - but for what it's worth the 1932 war loan pays an implicit interestrate of 3.9% at its current price.
Right now, he sees vast similarities between the bond market today and the low-interest rate world with high debt-to-GDP after World War II that led to a generational bear market in bonds.