Frankfurt, the cathedral area in ruins after Allied bombings March 31, 1945, U.S. Army photo. The area shown is about 2.5km SSE of the high school. The USAAF bombed during daylight so they could see what they were doing, unlike the British who bombed at night and didn't care who or what they hit. At first the US bombers tried to hit only military targets. But towards the end of the war numerous cities including Frankfurt were virtually wiped out by the USAAF as well as the RAF. The Americans, however, always advocates of "precision bombing"[1], managed to avoid hitting the Dom, the Bahnhof, and the I.G. Farben building. Nevertheless, the interior of the Dom was entirely burned out because of the surrounding fires; it was reconstructed in the 1950s[3]. The Dom was where the Holy Roman Emperors were elected, 1356-1792, and where they were crowned from 1562.

[See leaflet dropped on Frankfurt by RAF]

Unlike London and Berlin, Frankfurt did not have a subway to shelter in, but it did have a network of virtually indestructible above-ground bomb shelters[8] as well as at least one bunker hospital[4]. Also, numerous buildings had reinforced basement shelters (ausgebaute Schutzkeller)[8], often connected by makeshift tunnels for alternative escape routes. The death toll from the bombing in Frankfurt was 5,500[5] out of a population of about 550,000[6], a much lower death rate than in cities such as Hamburg, Dresden, Kassel, and Darmstadt where there were firestorms[7].

1. Donald L. Miller, Masters of the Air, Simon & Schuster (2006).
2. Davis, Richard G., Bombing the European Axis Powers - A Historical Digest of the Combined Bomber Offensive 1939-1945, Air University Press, Maxwell Air Force Base, Alabama, April 2006, 652 pages. Covers the Allied bombing offensive in detail, including all the raids on Frankfurt.
3. Frankfurter Dom, Wikipedia.
4. Hospitals in Air Raid Shelters - 'Bunker Hospitals':  Frankfurt am Main, Offenbach am Main, Mannheim am Neckar, US Naval Forces, Germany, Technical Section (Medical), 1945, 60 pages (the first six are blank). The first section describes a 488-bed bunker hospital in Frankfurt in great detail, complete with photographs, but does not seem to mention exactly where it was, or if it was the only one of its kind (but see [8]):
5. Bombing of Frankfurt am Main in World War II, Wikipedia (accessed 10 September 2019).
6. Timeline of Frankfurt, Wikipedia (accessed 10 September 2019).
7. Firestorm, Wikipedia (accessed 10 September 2019).
8. Bunker in Frankfurt am Main, bkffm.siemavisuart.de/bunker/bkfra.html, accessed 25 February 2020. Thanks to Klaus Peter Laatz for referring me to this site.
9. Armin Schmid, Frankfurt im Feuersturm, Verlag Frankfurter Bücher (1965). A thorough and detailed account of the bombing of Frankfurt as well as the deportation of its Jews, with many photographs.
10. Martin Nicolaus, Memories of Frankfurt (1945-1953).
11. Hans Jürgen Massaquoi, Destined to Witness, Harper Perennial (1999), p.142 (about the air-raid shelter construction program).