For all countries using a U.S. type banking system, there isn't any national debt. It's a misnomer. It's a lie.
National debts are moneys supposedly owed to the central bank. In the case of the U.S., it's the Federal Reserve Bank.
Why is it a lie? The system was legislated to make it look like money was borrowed from the bank. In reality, the loans were creations of new money that were supposed to ultimately wind up in the hands of those people who "borrowed" the money. In reality, when the people supposedly borrowed the money, they actually created it, not borrowed it.
The idea was to always allow enough money to cover the number of people in the nation as the population grew. There might not be enough gold and silver to do this. That's why we needed a different system than gold and silver only.
The major flaw in this system is, the banks never return the money to the people. Thus, if there is any debt, it is the debt of money owed to the people by the banks. This debt amounts to all the money and interest that the people ever paid to the banks as loan payments.