This question depends on how bombers were used. The British and Germans utilized night time bombing missions so visual bomb sights were not as useful to them. They both opted for radio beam technology which both guided their bombers to the target and informed them when to drop their payloads. The Germans used this technology from the beginning of the war in 39, the British while always flying night time missions converted to their own brand of beaming technology later in the war. The United States philosophy was to defend their bombers in the air, and fly daylight missions which they felt were more accurate and reliable in hitting the target. The United States tried different strategies to defend their bombers in daylight before settling on long range fighter escorts with extra large drop tanks.
The problem everyone was trying to counter was Bombers were slow vulnerable cumbersome beasts, vulnerable to fighter intercepters. This vulnerability was negated by night time bombing. Even large slow moving bombers could fly safely across Europe or the UK with a coat of dark paint and a sufficiently high altitude. Problem was such high flying nighttime missions while safer for the bombers were not very accurate at hitting targets smaller than cities, and even cities proved difficult when they were blacked out. Which meant nighttime bombing without electronic aids was largely a terror weapon, not a strategic weapon.
To negate this shortcoming, the Germans used sophisticated radio beaming technology. First the Germans used a system called Knickebein. One beam would determine the path of the bombers. If the bombers were to the right or left of the beam, radio's in their pilots ears would inform them with a series of dots(turn right) or dashes (turn left). An intercepting beam would tell the bombers when to drop their bombs. The British code named the German knickebein system "head-ache" and their countermeasures were code named "aspirin". The British struggle to identify and counter this German system was known as the "Battle of the Beams".
The knickenbein system had a number of short comings. The beam was relatively easy for the British to identify once they started looking, and the system was not designed to direct large formations. These shortcomings were addressed when knickenbein was replaced by the more accurate, better ranged, and harder to detect X-Gerät system, which also used Radio beaming technology. X-Gerät used a more focused beam which was more difficult for enemy countermeasure craft to find. More focus also meant more accuracy.
The British adopted similar systems to the German Knickenbein and X-Gerät systems which also relied upon radio beaming technology(Gee and Oboe).
From late 1943 the RAF used two radar-beam systems called Gee and Oboe to guide its Lancaster and Halifax bombers to cities on the Continent. In addition, the bombers carried a radar mapping device, code-named H2S, that displayed reasonably detailed pictures of coastal cities such as Hamburg, where a clear contrast between land and water allowed navigators to find the target areas.
The United States was not a fan of night time bombing. While safer for the bombers, prior to the development of allied beaming technology night time bombing compromised the accuracy and effectiveness of the missions.
They opted instead to use a sophisticated bomb sight which relied upon visual markers to determine the plane's true ground speed, and then mechanically adjust the targeting apeture to account for altitude and speed. This device was named the Norden Bombsight. The Norden bombsight was pretty accurate in ideal conditions, but was subject to problems from rain, fog, or cloud cover all of which could be sufficient to scrub entire missions. The Norden Bombsight was also notoriously complex and difficult to use.
An additional benefit of American daylight missions was that the allies could conduct missions 24 hours a day, with the RAF conducting night time raids. The United States used the Norden Bombsights in both theaters of WWII, Korea and Vietnam. Both nuclear devices dropped on Japan were dropped utilizing the Norden Bombsight.
To counter the vulnerability problems of bombers the Americans first tried to fortify its bombers. The theory was fortified bombers in tight formations would be able to defend themselves from enemy fighters. Fortifying the bombers though made them heavier and slower; ultimately this tactic was not effective in countering the dangers of enemy fighters.
In fall 1943, the 8th Air Force's heavy bombers conducted a series of deep-penetration raids into Germany, beyond the range of escort fighters. The Schweinfurt–Regensburg mission in August lost 60 B-17s of a force of 376, the 14 October attack lost 77 of a force of 291—26% of the attacking force. Losses were so severe that long-range missions were called off for a time until an effective escort could be found.
The P-51 mustang with an extra large 80 gallon drop tank would become the bomber escort the United States were seeking. It saved both the American concept of daylight bombing and for that matter the utility of the Norden bombsight with it's ability to protect daylight missions.