The US was afraid that the first bomb wouldn't explode properly because of its high failure rate. If the first use of this super weapon had been a dud, they fea

The US was afraid that the first bomb wouldn't explode properly because of its high failure rate. If the first use of this super weapon had been a dud, they feared that this would feed into Japanese propaganda, and a second bomb wouldn't have the same shocking effect anymore. Since they were unable to produce many of these bombs for months, the first two had to do.