The new two-way aerial assault on the Nazis, which has seen 17 major attacks on German cities in two weeks, was intensified yesterday with two new blows at important industrial centers within 12 hours -- an RAF night attack on Kassel and an Eighth Air Force bombing of Frankfurt in daylight yesterday.
    Kassel, 100 miles east of last week's much-battered Ruhr, is the site of one of the few German aircraft plants not previously hit in such raids as the American attacks on Vienna, Regensburg and Paris. Kassel also is the site of the Henschel locomotive and automobile works and is a big railroad center.
    The Fortresses' target at Frankfurt, 100 miles southwest of Kassel, is one of Germany's prime cities, replete with high priority objectives on which the Allied air chiefs have been concentrating recently -- rubber, auto and chemical factories and railroad concentrations.
    Fifteen bombers were lost and 56 enemy fighters were destroyed, headquarters said.
    It was the first American raid on Frankfurt, bombed many times by British heavies since the start of the war. The city is on the right bank of the Main River, about 420 miles from Britain. It has a population of more than half a million.

    Preliminary reports of the Frankfurt raid gave no indication last night of the opposition encountered or the damage done, but some returning crews said they were "puzzled" by the lack of German resistance on the way in. Neither fighter nor flak opposition was heavy, they said, until the Forts had made their bombing run and were headed for the coast -- a further indication of the success of the recent concerted assault on Nazi fighter factories and airfields.
    One unconfirmed report last night said that a single Flying Fortress had accounted for 11 enemy fighters, a record, if true.
    Headquarters announced that P47s had shot down 19 fighters while escorting the Forts. An unofficial report said two Thunderbolt pilots scored three each. None of the U.S. fighters was lost.
    Among the Fortresses in yesterday's raids was the newly christened Stars and Stripes, named for this newspaper. Sgt. Charles F. Kiley, of Jersey City, N.J., a staff writer who has qualified as an air gunner for such assignments, "covered" the raid from the nose of the B17. Sgt. Andrew A. Rooney, of Albany, N.Y., another staff writer who has made several previous missions, was in another plane in the same squadron to assure coverage.
    The assault on Kassel was the fourth big blow in six months on that manufacturing center for Messerschmitt fighter planes, locomotives and other war machines.
    The Kassel attack was described officially as heavy and cost 24 bombers.
    Kassel, a city of more than 200,000, has been bombed more than a dozen times during the war -- twice by Fortresses, July 23 and July 30 -- and the raid Sunday night was the fifth on Germany in seven nights by British-based bombers. The multiple targets hit made an average of more than one city a night for two weeks.
    At Kassel are the Fieseler aircraft works, which the hard-pressed Nazis have been forced to shift from the original product of light cub army observation planes to Messerschmitt fighters, because of the inroads on combat plane sources such as the recent Fortress attacks on fighter factories at Vienna, Regensburg and Paris.
    In addition to the Kassel raid, RAF Mosquitoes bombed Hanover and objectives in the Rhineland, and other planes laid mines in enemy waters. Australian Mosquitos destroyed one Ju88 and damaged three enemy patrol boats in the Bordeaux area.
    The heaviest fighter attacks in yesterday's raid were borne by a formation of five Flying Fortresses, which, separated from the big aerial armada, went on to make their own bomb runs over the railway yards at Frankfurt and then fought back to base through nearly a solid hour of fighter attacks and heavy flak.
    One of the five Forts -- Weider's Wildcat -- claimed four enemy fighters destroyed in a running battle which left the plane with more than 100 bullet, cannon and flak holes; with the left elevator completely shot away, the left stabilizer in shreds, and landing-gear tires minced by 20mm. shells and flak.
    S/Sgt. Elmer F. Congdon, waist gunner from New Haven, Conn., shot down an Me109F and saw the Nazi pilot plummet to earth when his parachute failed to open. S/Sgt. Alfred W. Spencer Jr., Wyandotte, Mich., tail gunner, said seven FW190s attacked the plane's tail in formation. Spencer's first burst blew one of the enemy ships apart and the other six fled.
    T/Sgt. Stanley Robinson, of Pawling, N.Y., top turret gunner, chopped up a 109F, shooting its tail assembly completely off the fuselage. S/Sgt. A. J. Guinta, ball turret gunner from New York City, destroyed a Me109F, which tried a sneak attack from directly beneath the ship.
    Weider's Wildcat had a complicated day. The pilot, Norman L. Weider, of Richmond Hills, N.Y., came back from the raid to find he'd been promoted to 1/Lt. while he was away. When the ship took off in the morning it was known as Lucky Strike. After their battle on the way home, the crew decided it had used up all the luck in the name and swapped titles.
    2/Lt. Ernest Bemis, from Bridgewater, Mass., co-pilot of the Vibrant Virgin, said it was plenty rough in spots with fighters making quick passes and exceptionally large flak bursts.
    S/Sgt. Robert Mixon, a ball turret gunner from Yemessee, N.C., said: "Nothing happened between the base and the target, but as we were getting ready to bomb we ran into a mess of fighters. A ship from another group was downed. On the way home the German flak, which had been noticeable by its absence on the way in, really came up at us. It was tough."
    Most of the crews told of encountering Me109s. There were some two-engined fighters, but most were Me109s.
    The Hootin' Nanny, piloted by 2/Lt. Carl Dawurske, of Sheboygan, Wis., managed to stagger back to England with its controls shot away. All of the crew bailed out safely on English soil.