Actually he's designing a 4 dton missile with a 1 dton nuclear/bomb pumped warhead.
Again, I am resurrecting an old thread to add some information to it.
One Traveller dTon is circa 500 cubic feet. Now, there are just under 7.5 gallons in a cubic foot, so 500 cubic feet would hold about 3750 gallons of liquid. To visualize a Traveller dTon, think of a 10,000 gallon tank truck, and then cut it into thirds. Each third would be about a Traveller dTon.
Given that much volume, you probably could build a 25 to 50 megaton bomb in it, assuming a fission-fusion-fission weapon. With very good design, you probably could get it up to maybe 100 megatons. That is a very serious bomb.
A World War Two 4,000 pound Light Case bomb, loaded with about 3200 pounds of TNT had a total destruction radius of 120 feet against European-style brick construction, and a visible damage radius of 265 feet. Now, that would be affected by exactly where the bomb detonated. If in an open street, then that type of damage could be expected. If loaded with Torpex, an aluminized RDX-TNT mixture, that damage radius would be increased by 25 percent. Torpex had about twice the blast effect of TNT. Against a flammable target. such as the Japanese cities, the same weight of incendiaries was 5 times more effective at inflicting damage than straight high-explosive bombs. The single most destructive air attack in World War 2 was not either the Hiroshima or Nagasaki bombs, but the March fire bomb attack on Tokyo. The Army Air Force did expend considerable effort on bombing Japanese refineries that was not in operation due to a lack of crude oil to refine.
The USS Stark was hit by an Exocet missile, with a warhead of about 150 kilograms, half of which would have been explosive, with the warhead functioning correctly. During the Iraq-Iran War, the Exocet's warhead did not always explode properly, resulting in tankers with un-exploded missiles in them, the tankers were scrapped rather than trying to deactivate or remove the missile. The Exocet that hit the HMS Sheffield during the Falklands Island War did not explode either, but did hit a reserve feed tank for the ship's turbine engines and the resulting fire inflicted fatal damage on the ship when the attempt was made to tow it to South Georgia Island.
The damage to the USS Cole was caused by a near-contact blast of equivalent to about 500 pounds of TNT.
The Grand Slam bomb of World War 2 that was mentioned did not explode on the surface, but was intended to penetrate into the earth and then explode, destroying the buildings by ground shock, in addition to causing a very impressive crater. Post-war, the U.S. Air Force adopted the 12,000 pound Tall Boy, and for a short period was using a guided version of the weapon, called the Tarzon, in Korea. It had quite good accuracy when used by a skilled crew.