The U.S. Air Force， unlike the Navy， was determined to improve bombing accuracy even during the Vietnam War. Before that conflict was over， it had developed and used the first of its guided-bomb systems1. This was used to good effect in attacking pinpoint2 targets that had previously resisted conventional attacks（and had gotten many Air Force bombers shot down3 by dense4 defenses）。 The Air Force continued working on better bombing systems throughout the l970s and l980s. This was an expensive proposition， but then， the Air Force spends more of its budget5 on research and development than the other services. The wisdom of this effort did not become obvious until the Gulf War6 when it was found that the Navy aircraft， lacking such systems， were much less effective.
To put this into perspective7， consider what it took—— in three wars， over the past fifty years—— to achieve a 90 percent probability8 of destroying a target measuring sixty feet by one hundred feet （a building， usually housing a headquarters， factory， or whatever）。 In the 1940s （World War II） this required 1，500 heavy bomber9 （B-17） sorties10 dropping 9，000 one-ton bombs （half of which would land more than 3300 feet from the target）。 In the 1960s （Vietnam） more accurate bombing systems allowed the same target to be destroyed with 176 jet fighter-bomber （F-4 Phantom11） sorties， each carrying one bomb （half of which would land more than 400 feet from the target）。 In the l990s （Iraq） this required one sortie by a light bomber （the F-117A Stealth12）， carrying a single one-ton bomb that will land within ten feet of where it is aimed.
A painful lesson from Vietnam was the high cost of attacking heavily defended targets. These losses could be reduced by sending along swarms13 of electronic warfare aircraft and bombers to destroy the enemy radars and antiaircraft14 weapons. Precision bombing systems also made the losses more tolerable15. The Air Force theorized that it would be even more efficient to develop aircraft that would be relatively invisible to enemy radar. Thus these " stealth" aircraft （designed to be nearly invisible to enemy radar） could go in alone and either bomb high-value targets or destroy the enemy air defenses. Also， when they were loaded with precision guided bombs， the Air Force would have a practically invulnerable16 bomber that would not only reduce friendly losses but also reduce the losses of enemy civilians. The first of these stealth aircraft was the F-117. Built in secret to deny potential opponents the opportunity to develop countermeasures17， the F-117 became operational in the early l980s and did not get its first real trial by combat until the Gulf War. While the F 117A was called the " stealth fighter" ， it was actually designed and used as a light bomber. The mission it was designed for was to penetrate18 thick Soviet air defenses in Central Europe and attack key targets and air defense systems （radars， command centers， and missile launchers）。 The Iraqi air-defense system was built with Soviet assistance and largely with Soviet equipment. The F-117A had little trouble dealing with it. Production of the initial batch19 of F-117As was completed in the late l980s.
Meanwhile， another " black" （secret） project， the B-2 bomber， was also built using stealth technology. The B-2 is an enormously expensive aircraft as it contains even more advanced stealth technology， carries much more weight in bombs， and has a much longer range. The cost of this program makes it difficult for the Air Force to justify building more than a handful of B-2s. The Air Force has other stealth projects that deal with reconnaissance20 work.
与海军不同，美国空军早在越战期间就决心提高其轰炸精度。越战结束前，空军就研制并率先使用了制导炸弹系统。该系统用于攻击定位精确的目标时的效果很好。这种目标先前难以用常规攻击方式加以摧毁（空军的许多轰炸机被密集的防空炮火所击落）。在整个70年代和80年代，空军一直在研制更好的轰炸系统。该项目耗资巨大。空军用于研究与开发的经费比其他军种多。这样做的高明之处直到海湾战争才显露出来。当时，海军的飞机由于没有装备这种系统，轰炸效果要差得多。
让我们分析一下在过去50年里发生的3次战争，轰炸一个长100英尺宽60英尺的目标（通常是一幢可容纳一个指挥所、一家工厂或其他单位的大楼），毁伤概率为90％，需要多少飞行架次和投掷多少炸弹：在40年代（二战时期），需出动重型轰炸机（B-17）1500架次，投掷1吨重的炸弹9000枚（有一半炸弹偏离目标3300多英尺）；在60年代（越战期间），由于使用更为精确的轰炸系统，摧毁同样目标只需出动喷气式战斗轰炸机（F-4"鬼怪式"） 176架次，每架飞机携带1枚炸弹（其中一半炸弹偏离目标400多英尺）；在90年代（海湾战争期间），仅需一架轻型轰炸机（F-117A隐形飞机）出动 1个架次，该机只携带1枚1吨重的炸弹，炸弹将落在所瞄准目标的10英尺范围之内。
越战中的一个惨痛教训是，空军飞机攻击敌严密防卫的目标时伤亡惨重。要减少损失，可出动大批电子战机和轰炸机摧毁敌人的雷达和防空武器。使用精确轰炸系统也可将损失减少到较能承受的程度。空军的理论是，发展那种使敌人雷达难以发现的飞机，是减少飞机和人员伤亡的更为有效的途径。这样，设计成几乎让敌方雷达看不到的"隐形"飞机，便可单机在有重要轰炸价值的目标区轰炸或摧毁敌防空体系。"隐形"飞机一旦装有精确制导炸弹，空军就拥有了一种实际上难以摧毁的轰炸机。这种飞机不仅能减少己方的伤亡，而且还能减少敌方平民的伤亡。第一种隐形飞机是F-117.为防止对手研制出对抗设施，F-117的生产十分保密。该飞机于80年代初开始投入使用，而首次真正接受作战检验还是在海湾战争中。虽然F-117A被称为"隐形战斗机"，实际上它是被作为轻型轰炸机来设计和使用的。其任务是突入苏联在中欧的严密的防空体系，对重要目标和防空系统（雷达、指挥中心和导弹发射架）实施攻击。伊拉克的防空系统是在苏联的帮助下建成的，所使用的装备主要是由苏联提供的。F-117A型飞机对付它毫不费事。F-117A型飞机最初的批量生产完成于80年代末期。
与此同时，另一项采用隐形技术制造B-2轰炸机的"黑色"（秘密）计划也已开始。B-2轰炸机由于使用了更先进的隐形技术，所以造价十分昂贵。该机的载弹量要大得多，航程也远得多。昂贵的造价使空军难以找出批量生产B-2轰炸机的充足理由。空军还拟定了在侦察工作方面使用隐形技术的其他一些计划。
注释：
1.guided-bomb system 制导炸弹系统
2.pinpoint adj.[军]定位精确的
3.shot down 击落
4.dense adj.密集的，浓密的
5.budget n.预算拔款，专款
6.Gulf War 海湾战争
7.perspective n.视角，想法
8.probability n.[数]概率
9.heavy bomber 重型轰炸机
10.sortie vi.（军用飞机）出动，出击
11.phantom n.幽灵，[P-]鬼怪式飞机
12.stealth n.秘密行动[S-]隐形飞机
13.swarm n.蜂群，一大群
14.antiaircraft adj.防空的
15.tolerable adj.可容忍的
16.invulnerable adj.不会遭到攻击的
17.countermeasure n.对策，反措施
18.penetrate vt.穿透，突破
19.batch n.一批生产量
20.reconnaissance n.侦察