The United States has been reluctant to provide data on the results of the air campaign against ISIL (Islamic State in Iraq and the Levant) in Syria and Iraq. In part this reticence results from that face that it is difficult to send in troops to check the damage (as was common in Afghanistan and Iraq) because there are so few American troops in Syria and Iraq these days. Yet the United States has extensive intel resources (aerial and on the ground) that obtain a lot of useful information about what is happening on the ground but you don’t want to make that data public because it risks revealing details of how it reached any of its conclusions. The evasiveness was understandable because if the enemy can find out who American informants are or how sensors work that would risk making methods less useful. Informants can get killed and the enemy can develop tactics to hide from sensors. In general intelligence organizations will not make public information on methods and sources because, at the very least, this makes the, more difficult to use effectively the next time around.
But there is one bit of information the United States has been releasing for a long time and that is the number of missions in which weapons were used. This has become a much more useful bit of data since the 1990s when the United States and most Western nations stopped using unguided bombs and switched to smart (guided) bombs and missiles. Along with that came an unprecedented drop in civilian casualties when airborne weapons were used. This led to stricter and stricter ROEs (Rules of Engagement). As a result, after 2001 each aerial weapon used was almost always hitting what it was used against and doing damage.
Thus while the number of warplanes used over Syria and Iraq has not changed much since the bombing campaign began in 2014 the ROE has. Thus the number of weapons “released” is telling. There were 269 weapons used in August 2014 and this rose to 1,888 in December 2014 then to 2,823 in July 2015. By the end of 2015 it was over 3,000 a month and headed for 4,000. The increased weapons count correlated with the growth in ISIL deserters and civilians who escaped ISIL territory reporting higher casualties from air strikes.
The U.S. gradually loosened up its ROE in 2015 and accelerated this after October when Russian warplanes began operating in Syria. The Russians had a much less strict ROE and their air attacks were doing far more damage to ISIL and other rebel groups despite the heavy use of human shields by ISIL. All this led to more dead civilians but the amount of damage done to ISIL increased so much that in the last year ISIL manpower in Iraq and Syria has declined about 20 percent.