Robotic aircraft, ground vehicles and ships are taking a rapidly growing share of the arms market. UAV (unmanned aerial vehicles) are already more than ten percent of combat aircraft sales, and by the end of the decade that will more than double to over 20 percent of sales. Depending on how rapidly flight software and control systems of combat UAVs mature (and become more reliable), that percentage will grow even faster. Most combat aircraft designers and manufacturers have agreed that what they are currently working on is the last generation of manned combat aircraft. The future belongs to UAVs.
Meanwhile, it's uncertain if UUVs and USVs (unmanned subs and surface ships) will ever really take off. Optimists see these vessels gaining sales of at least several billions of dollars a year by the end of the decade. But, while the technology is there, and working models are in use, UUVs and USVs have not yet attracted heavy sales.
Ground based UGVs are also successful, but not taking a big bite out of defense budgets. UGVs racked up about $400 million in sales last year, versus about $6 billion for UAVs. By the end of the decade, that should increased by 4-5 times. But much depends on acceptance of armed UGVs. Israel is using some for border patrol, but no one else is. The U.S. has bought thousands of smaller, and unarmed UGVs for bomb disposal and some infantry and security tasks. There are plans for larger combat vehicles, and if these ever show up in a useful form, then there will be bigger sales numbers. Another breakout market is for unmanned support vehicles (trucks). If the reliable tech shows up, the sales will follow.