Those one ton shells or bombs would leave a crater five meters deep and 10 meters wide. The blast effect would kill or disable any troops within 300 meters of the impact (and bang you up pretty bad for twice that distance.) The high explosive shell could penetrate up to ten feet of concrete, more if an armor piercing shell was used. The shells were also relatively cheap, costing about $8,000 ($20,000 if you count the cost of the propellant and cost to replace the barrel, which has to be done after about 300 shells are fired). Smart bombs cost a lot more, although the price has been cut some 90 percent over the last three decades to about $25,000 (current price).
But there was nothing quite like the 16 inch gun. Once an enemy knew you were using it, they knew they had a choice of either dying in the wreckage of their bunkers, surrendering to fleeing. There was no defense. But the battleships are all gone now. They were too expensive to operate, even though the infantry and marines strongly urged that the battleships be kept in service. The last battleship was retired in 1998. Things looked pretty grim for the guys fighting on the ground. While there is plenty of 155mm artillery, and these guns fire 90 pound shells that can do a lot of damage, they are not as decisive as the 406mm (16 inch) gun. The army has it's MLRS rockets, but these are expensive. Most use cluster bomb technology. This means each rocket carries many little bombs (up to 950). Great for troops or equipment out in the open, but not for the infantryman's nightmare; enemy troops dug in or bunkers. The closest thing the Army had was the larger ATACMS rocket, which was the equivalent of a 500 pound bomb, but cost $700,000 each.
Salvation came from an unexpected quarter. The U.S. Air Force had continued to produce cheaper and more accurate smart bombs. By the 1990s it had several models that used GPS (assisted by a back up Inertial Navigation System.) The GPS had an average miss distance of 13 meters. If the GPS was jammed, the unjammable INS could do it alone, but with only 30 meter accuracy. But this was a lot more accurate than the 16 inch gun, and it delivered the same weight. But there was another difference. A one ton high explosive bomb contained about five times as much explosive as a high explosive 16 inch shell. This was because the shell required thicker metal construction to survive getting fired out of a rifled barrel. This actually made the bomb more destructive than the 16 inch shell, for the blast was bigger and for most enemy fortifications, the damage was greater. It also turned out that these bombs really scared the hell out enemy troops under the right circumstances. And those turned up, unexpectedly, in Afghanistan.
The air force saw the more JDAM bombs as a better weapon for hitting what the air force like to hit; buildings. These could be enemy headquarters, air defense bases, hangers, transportation structures and the like. At first, that's what the navy and air force warplanes hit in Afghanistan. But then the army special forces troops got on the ground and hooked up with the Northern Alliance forces. What was holding up the Northern Alliance was the Taliban fortifications. Without enormous quantities of tanks and artillery, the Northern Alliance was not going to overcome these trenches and bunkers. Moreover, the Taliban had more troops. The special forces, however, quickly realized that a one ton bomb here, and another one there, directed at specific Taliban fortifications, would enable the Northern Alliance men to advance. The air force went along, although they never thought they'd be using one ton bombs, dropped from B-52s, to provide close support. But the high accuracy of the JDAM allowed the Northern Alliance troops to get close enough to the Taliban positions (well, half a mile or so, to insure the Northern Alliance lads didn't get stunned by the blast) to rush in once the Taliban had been killed or rendered senseless by the 2000 pound JDAMs.
Now the ground troops have their battleship guns back in the form of JDAM. As long as the air force is able to maintain air superiority (which they and the navy have consistently done for over half a century), the heavy bombers can circle in the sky while the infantry down below carefully direct the one ton bombs in the most efficient manner. Even if the enemy air defenses are strong, there is a longer range smart bomb (JSOW) that can be dropped away from front line surface to air weapons. Jamming GPS will become more popular, but that can be defeated and JDAM/JSOW have back up systems that can't be jammed. For the moment, ground combat has undergone another one of those major changes, as when the machine-gun and tanks showed up. And this time, most of the time only one side will have the wonder weapon.
Infantrymen have a love/hate relationship with artillery. They love it, because if they have a lot of big guns supporting them, they can blast the enemy and then advance against a lot less resistance. But being on the other end of that situation is decidedly unpleasant, and often fatal. American troops have, for the past sixty years, usually had a lot more artillery supporting them than their opposition. But not all artillery is equal. Artillery comes in many different sizes, from 81mm mortars firing 15 pound shells, to 16 inch naval guns firing 2200 pound shells. Naturally, any soldier or marine who has been supported by those naval guns, will tell you that bigger is definitely better. What made the 16 inch gun so effective was that those 2200 pound shells could smash just about any enemy fortification. Compared to 2000 pound bombs dropped from aircraft, the 16 inch shells were ten times more accurate during World War II, when lots of battleships were available. The shells would land within 110 meters of where they were aimed. But after World War II, the bomber became more accurate. One ton bombs dropped by modern fighter bombers (a $10-40 million dollar aircraft) during the 1991 Gulf War got their accuracy down to 60 meters, mainly though the use of smart bombs. But the air force wasn't willing to risk it's aircraft regularly bombing the front lines. It's couldn't afford to, for the more expensive fighter bombers meant that it had a lot fewer aircraft than during World War II.