Battlefields are deadly places, even after the fighting is over. Leftover weapons still retain the ability to kill and maim.

This became a really big problem when gunpowder weapons came along several centuries ago. Before too long, some cannon balls were filled with gunpowder - these came to be called "shells." When the fuse meant to detonate the gunpowder failed to work, the shell became known as a dud. But the dud was deadly if someone came across it later and accidentally set off the gunpowder. Farmers would find these shells, try to melt them down for the metal and, boom, more casualties.

In the 20th century, most artillery ammunition comprised shells, and they had better fuses. While this meant there were fewer duds, those duds were more deadly. The modern fuse could be activated if the "dud" shell were dropped or simply picked up and moved. Added to the shells were hand grenades, bombs, mines and explosive charges used to blow up all manner of battlefield targets. A percentage of all these explosive devices became duds.

In the first half of this century, hundreds of millions of fused devices were used in combat, and five to ten percent of them were duds. In Europe, the site of heavy fighting in two world wars, dozens of people still are killed or injured each year by duds.

In the last few decades of this century, it got worse. The reason was submunitions, smaller bombs carried inside a container. The idea was that when the shell or bomb carrying submunitions was used, it would spread these smaller bombs over a larger area and do more damage than one large explosion. It worked, but it also created more duds. Not just more, but smaller duds. Small enough for children to pick up and start playing with. Kids are more adventurous and less well informed than adults. A dud submunition looked like a new toy.

It got still worse. Submunitions turned out to have a higher dud rate than any previous weapon. New artillery shells have a dud rate of about two percent. Israel went so far as to fire 10,000 new shells to confirm that dud rate. But many nations stockpile shells and as these grow older, their dud rate increases. Shells actually have an expiration date, reflecting the fact that the chemicals in the explosives and the fuses grow unstable as they age.

The Third World and communist nations often had poor quality control to begin with, and were more prone to keep old ammunition. During the Afghanistan war of the 1980s, Russian shells appeared to have a dud rate of some 30 percent. And even the United States would sometimes use submunitions that had exceeded their recommended shelf life.

Submunitions were designed originally to have a dud rate similar to that of artillery shells. But in practice it was much higher, closer to five percent. Part of reason for this is the lighter weight of submunitions. Shell fuses detonate a shell when it hits the ground. The impact sends a pretty strong message to the fuse that now is the time to do it, and go bang. But submunitions, weighing from a few ounces to a few pounds, can make a soft landing, and not generate enough force to activate the fuse. These make even deadlier duds, for the fuse is not defective, just deceived. When enough force is applied to activate the fuse, you have an explosion. The dud rate got higher depending on where the submunitions landed. In winter, with snow on the ground, the dud rate was as high as 15 percent.

When these high dud rate problems were discovered in the early 1980s, several solutions were at hand. More complex, expensive and reliable fuses were a possibility. But research showed that to halve the dud rate would double the cost of a submunition. To bring the dud rate down to one percent would quadruple the cost. At the time, submunitions cost about five bucks (in current dollars).

In the United States, the largest manufacturer of submunitions, no change was made through the 1980s. To use the more expensive fuses would have meant buying fewer munitions. But the Gulf War of 1991 showed that all those dud submunitions tended to cause a lot of casualties among your own troops. The reason was simple. As you would fire a lot of submunitions at the enemy, and then overrun the enemy positions, your troops would suddenly find themselves amidst all those duds. Friendly casualties were the result.

Israel and Germany, who both manufactured their own submunitions, went for the safer fuse. Better designs brought the cost down, and they ended up paying $10 to $15 for each submunition. But they achieved dud rates of less than one percent. The safer fuse was basically a self-destruct device. If the submunition did not explode as it was supposed to, another fuse detonated it within 14 to 18 seconds.

Even with the better fuses, submunitions still are more dangerous after the battle than older shells. Fire 10,000 artillery shells (a typical quantity for a battle in an area covering a square mile or so), and you end up with a minimum of 200 dud shells, or as many as 3,000 if you are using old, poorly made stuff. But if you use the most modern submunition-equipped shells, you are putting 200,000 or more submunitions into the area, and a minimum of 2,000 duds. Fight this battle in the winter, with the older fuses, and you end up with over 50,000 duds. It's no wonder that most submunition fuses now are of the more expensive, and more reliable, variety.

Submunitions seemed a good idea at the time they were developed, but as with any other new weapon, there were dangers no one anticipated. And thousands of additional dud munitions littering the battlefield turned out to be a serious problem for which no one yet has found a satisfactory solution.

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