We likely couldn’t do any real damage, at that point on time.
Those moon craters were created by meteorites that hit it with more force than anything we can create at the time of this report and the moon is still their.
I believe we could actually split the moon and suffer no real I’ll effects, because the gravity forces would re-meld the moon.
Our largest thermonuclear weapons were developed and tested prior to 1959.
With the increasing accuracy of our delivery systems we were able to reduce the yields of the weapons and thus the requirements for the huge quantities of fissile materials needed to build them. The people who were responsible for the development and employment of nuclear weapons did not want massive weapons, only ones big enough to perform required tasks needed to fight a war and thus deter our enemies from starting one.