Editing Rockwell B-1 Lancer (section)

===Design studies and delays===
Although effective, the B-52 was not ideal for the low-level role. This led to a number of aircraft designs known as [[penetrator (aircraft)|penetrators]], which were tuned specifically for long-range low-altitude flight. The first of these designs to see operation was the supersonic [[General Dynamics F-111 Aardvark|F-111]] fighter-bomber, which used variable-sweep wings for tactical missions.<ref>Gunston 1978, pp. 12–13.</ref> A number of studies on a strategic-range counterpart followed.

The first post-B-70 strategic penetrator study was known as the Subsonic Low-Altitude Bomber (SLAB), which was completed in 1961. This produced a design that looked more like an airliner than a bomber, with a large swept wing, [[T-tail]], and large [[turbofan|high-bypass engines]].<ref>Taylor, Gordon. [https://apps.dtic.mil/dtic/tr/fulltext/u2/330289.pdf "Subsonic Low Altitude Bomber"] {{Webarchive|url=https://web.archive.org/web/20210419072226/https://apps.dtic.mil/dtic/tr/fulltext/u2/330289.pdf |date=19 April 2021 }}, Wright-Patterson Air Force Base ASD-TDR-62-426, June 1962.</ref> This was followed by the similar Extended Range Strike Aircraft (ERSA), which added a [[variable-sweep wing]], then en vogue in the aviation industry. ERSA envisioned a relatively small aircraft with a {{convert|10000|lb|kg|adj=on}} payload and a range of {{convert|10070|mi|km|abbr=}} including {{convert|2900|mi|km|abbr=}} flown at low altitudes. In August 1963, the similar Low-Altitude Manned Penetrator design was completed, which called for an aircraft with a {{convert|20000|lb|adj=on}} bomb load and somewhat shorter range of {{convert|8230|mi|km|abbr=}}.<ref>{{harvnb|Pace|1998|pp=11–14.}}</ref><ref name="Knaack pp.575-6">{{harvnb|Knaack|1988|pp=575–576.}}</ref>

These all culminated in the October 1963 Advanced Manned Precision Strike System (AMPSS), which led to industry studies at [[Boeing]], [[General Dynamics]], and [[North American Aviation|North American]] (later [[Rockwell International|North American Rockwell]]).<ref>{{harvnb|Casil|2003|p=8.}}</ref><ref name="Knaack p.576">{{harvnb|Knaack|1988|p=576.}}</ref> In mid-1964, the USAF had revised its requirements and retitled the project as Advanced Manned Strategic Aircraft (AMSA), which differed from AMPSS primarily in that it also demanded a high-speed high-altitude capability, similar to that of the existing Mach&nbsp;2-class F-111.<ref name="Knaack p.575">{{harvnb|Knaack|1988|p=575.}}</ref> Given the lengthy series of design studies, North American Rockwell engineers joked that the new name actually stood for "America's Most Studied Aircraft".<ref name=study>{{cite conference |conference=AIAA 16th Annual Meeting and Technical Display |doi=10.2514/6.1981-919 |first1=R.A |last1=Hibma |first2=E.D |last2=Wegner |title=16th Annual Meeting and Technical Display |chapter=The Evolution of a Strategic Bomber |date=12–14 May 1981 |chapter-url=https://arc.aiaa.org/doi/abs/10.2514/6.1981-919 |location=Long Beach, CA |access-date=7 April 2021 |archive-date=12 March 2022 |archive-url=https://web.archive.org/web/20220312092153/https://arc.aiaa.org/doi/abs/10.2514/6.1981-919 |url-status=live }}</ref>

The arguments that led to the cancellation of the B-70 program had led some to question the need for a new strategic bomber of any sort. The USAF was adamant about retaining bombers as part of the [[nuclear triad]] concept that included bombers, ICBMs, and [[submarine-launched ballistic missile]]s (SLBMs) in a combined package that complicated any potential defense. They argued that the bomber was needed to attack hardened military targets and to provide a safe [[counterforce]] option because the bombers could be quickly launched into safe loitering areas where they could not be attacked. However, the introduction of the SLBM made moot the mobility and survivability argument, and a newer generation of ICBMs, such as the [[LGM-30 Minuteman|Minuteman III]], had the accuracy and speed needed to attack point targets. During this time, ICBMs were seen as a less costly option based on their lower unit cost,<ref>{{harvnb|Pace|1998|p=10.}}</ref> but development costs were much higher.<ref name=Jenkins_1999_p21/> [[United States Secretary of Defense|Secretary of Defense]] [[Robert McNamara]] preferred ICBMs over bombers for the Air Force portion of the deterrent force<ref name="Knaack pp.576-7">{{harvnb|Knaack|1988|pp=576–577.}}</ref> and felt a new expensive bomber was not needed.<ref name=fas>[https://fas.org/nuke/guide/usa/bomber/b-1a.htm "B-1A page."] {{Webarchive|url=https://web.archive.org/web/20151122162355/https://fas.org/nuke/guide/usa/bomber/b-1a.htm |date=22 November 2015 }} Federation of American Scientists. Retrieved 20 March 2008.</ref><ref name="Knaack p.576-8"/> McNamara limited the AMSA program to studies and component development beginning in 1964.<ref name="Knaack p.576-8">{{harvnb|Knaack|1988|pp=576–578.}}</ref>

Program studies continued; [[IBM]] and [[Autonetics]] were awarded AMSA advanced avionics study contracts in 1968.<ref name="Knaack p.576-8"/><ref name=Jenkins_p23-6/> McNamara remained opposed to the program in favor of upgrading the existing B-52 fleet and adding nearly 300 [[FB-111A|FB-111s]] for shorter range roles then being filled by the B-58.<ref name="Schwartz p.119">Schwartz 1998, p. 119.</ref><ref name="Knaack p.576-8"/> He again vetoed funding for AMSA aircraft development in 1968.<ref name=Jenkins_p23-6>{{harvnb|Jenkins|1999|pp=23–26.}}</ref>