You might want take those documents with a grain of salt and read my post on modern armour piercing rounds. The IX had 22 mm thick pressure hull, and the VIIc/41 had 28-33 mm thick pressure hull.
I have some very detailed listings and after action reports on sinking of subs by US aircraft. None of the strafing attacks seriously damaged the U-boats, but sometimes cleared the deck allowing other aircraft to attack with bombs or rockets.
Here are a few examples:
U-966, 10 November 1943 (shared)
Type: VIIC Laid Down: 1 May 1942, Blohm &
Voss, Hamburg
Commissioned: 4 March 1943, Oblt. Eckehard Wolf
Commander: Oblt. Eckehard Wolf
Career: Assigned: March 1943–July 1943, 5th
Flotilla (Kiel) training; August 1943 –
November 1943 9th Flotilla (Brest)
Successes: None
Fate: Sunk 10 November 1943 in the Bay Biscay
near Cape Ortegal, Spain, by American and
Czech aircraft bombs in one of the longest
surface battles of aircraft against a U-boat in
WWII. At 0800, a VB-105 PB4Y-1 Liberator piloted
by Lieutenant L. E. Harmon was alerted
by an RAF aircraft of a radar contact near the
coast of Spain. Harmon located the surfaced
U-boat and made two strafing attacks. Heavy
AA fire damaged his aircraft and forced him to
break off the attack. An RAF fighter then dove
to attack the submarine. Harmon made a third
strafing attack, but had to break off afterwards
due to a fuel shortage. Lieutenant K. L. Wright
of VB-103 located U-966 near Ferrol at 1040
and delivered a strafing and depth charge attack.
Intense AA fire drove him off and he,
too, had to depart the target for lack of fuel.
Lieutenant W. W. Parish and crew then arrived
on the scene. A depth charge attack was conducted
in cooperation with a rocket-firing RAF
Liberator at 1230. The submarine was abandoned
by its crew after running aground at
Oritiguiera, Spain. The German crewmen
were quickly picked up by nearby Spanish
fishing vessels and interned in Spain.
Type: IXC Laid Down: 24 September 1940,
Deutsche Werft, Hamburg
Commissioned: 20 October 1941, Oblt. Georg
Staats
Commander: October 1941–November 1943,
Kptlt. Georg Staats (Knights Cross)
Career: Six Patrols; assigned: October 1941–June
1942, 4th Flotilla (Stettin); July 1942–November
1943 10th Flotilla (Lorient)
Successes: 14 ships sunk for a total of 74,087 tons
Fate: Sunk 12 November 1943, north of Cape
Ortegal, Spain, in position 46°00'N, 07°30'W,
by U.S. bombs (VB-103). 57 dead (entire crew
lost). Lieutenant (jg) Brownell made a night
attack on a submarine. His PB4Y-1 Liberator
was apparently heavily damaged by the Uboat’s
AA fire and crashed into the sea with
no survivors. The next day, two oil slicks
were spotted, about five miles apart. Postwar
examination of German records indicates that
he sank U-508.
U-598, 23 July 1943
Type: VIIC Laid Down 11 January 1941, Blohm &
Voss, Hamburg
Commissioned: 27 November 1941, Oblt.
Gottfried Holtorf
Commander: November 1941–July 1943, Kptlt.
Gottfried Holtorf
Career: Assigned: November 1941–July 1942, 8th
Flotilla (Danzig); July 1942–July 1943, 6th
Flotilla (St. Nazaire)
Successes: Two ships sunk for a total of 9,295
tons; one ship of 6,197 tons damaged
Fate: Sunk 23 July 1943, in the South Atlantic near
Natal, in position 04°05'S, 33°23'W, by U.S.
bombs (VB-107). 44 dead, one survivor.
Lieutenant (jg) Waugh, flying PB4Y-1 Liberator
aircraft 107-B-6, attacked the surfaced U-boat
in conjunction with a second squadron aircraft
flown by Lieutenant William R. Ford, sinking
the submarine. Waugh’s aircraft apparently
sustained damage during the attack, plunging
into the sea after his bombing pass with the
loss of all hands. The submarine’s identity was
confirmed by the sole survivor as U-598.
U-174, 27 April 1943
Type: IXC Laid Down: 2 January 1941, AG Weser,
Bremen
Commissioned: 26 November 1941, Fregkpt.
Ulrich Thilo
Commander: November 1941–March 1943,
Fregkpt. Ulrich Thilo; March 1943–April 1943,
Oblt. Wolfgang Grandefeld
Career: Assigned: November 1941–July 1942, 4th
Flotilla (Stettin); July 1942–April 1943, 10th
Flotilla (Lorient)
Successes: Five ships sunk for a total of 30,813
tons
Fate: Sunk 27 April 1943, south of Newfoundland,
in position 43°35'N, 56°18'W, by U.S. bombs.
53 dead (entire crew lost). A VP-125 aircraft attacked
U-174 on the surface near Cape Race.
The U-boat heavily damaged the PV-1 Ventura
with its 20-mm AA guns before sinking.
U-604, 30 July 1943
Type: VIIC Laid Down: 27 February 1941, Blohm
& Voss, Hamburg
Commissioned: 8 January 1942, Kptlt. Horst
Höltring
Commander: January 1942–August 1943, Kptlt.
Horst Höltring
Career: Six patrols; assigned: January 1942–July
1942, 5th Flotilla (Kiel); August 1942–August
1943, 9th Flotilla (Brest)
Successes: 6 ships sunk for a total of 39,891 tons
Fate: Lieutenant Commander Thomas D. Davies
and crew spotted a fully surfaced submarine
during a coastal barrier sweep northeast of
Bahia. The U-boat crew attempted to fight it
out with 20-mm AA fire, but the bow guns of
the Ventura quickly cleared the decks of the
submarine, allowing Davies to make a perfect
drop with four Mark 47 depth charges athwart
the still surfaced U-boat. The submarine, U-
601, submerged after the attack then surfaced
again at a 60-degree angle with the screws out
of the water. The U-boat then submerged
again. Later, German prisoners of war indicated
that the damage to the U-boat was so
severe that it had to be scuttled on 11 August
1943. The U-604 crew was taken aboard U-
185 and U-172 (during the sinking
U-615, 7 August 1943 (shared with VB-130)
Type: VIIC Laid Down: 20 May 1941, Blohm &
Voss, Hamburg
Commissioned: 26 March 1942, Oblt. Ralph
Kapitzky
Commander: March 1942–August 1943, Kptlt.
Ralph Kapitzky
Career: Assigned: March 1942–August 1942, 8th
Flotilla (Danzig); September 1942–August
1943, 3rd Flotilla (La Pallice)
Successes: Four ships sunk for a total of 27,231
tons
Fate: Sunk 7 August 1943, in the Caribbean southeast
of Curacao, in position 12°38'N, 64°15'W.
Lieutenant (jg) John M. Erskine, pilot of a
PBM-3S Mariner of VP-204, attacked the surfaced
U-615 on 6 August, causing moderate
damage. The squadron aircraft maintained
contact with the submerged submarine and
kept it down over night. On the morning of
the 7th, Lieutenant Anthony R. Matuski spotted
the U-boat when it surfaced and made an attack
run. His aircraft was damaged by return
fire and crashed with the loss of all hands.
Lieutenant Lewis D. Crockett, flying a VP-204
Mariner, located the U-boat and conducted a
bomb run that further damaged the vessel, but
resulted in severe damage to his aircraft from
AA fire. He remained on the scene until
Lieutenant Holmes, pilot of a PV-1 Ventura of
VB-130, arrived to assist him. The two aircraft
conducted a coordinated bombing and
strafing attack. Lieutenant (jg) John W.
Dresbach, in a VP-204 Mariner, arrived and
made a bombing and strafing attack on the Uboat.
This attack resulted in mortal wounds to
the pilot, Lieutenant Dresbach, and the final
blow for the submarine. A U.S. Navy destroyer
from Trinidad reached the area the next morning
and rescued forty-five of the U-boat’s crew
of 49.
U-572, 3 August 1943
Type: VIIC Laid Down: 15 June 1940, Blohm &
Voss, Hamburg
Commissioned: 29 May 1941, Kptlt. Heinz
Hirsacker
Commander: May 1941–December 1942, Kptlt.
Heinz Hirsacker; December 1942–August
1943, Oblt. Heinz Kummentat
Career: Assigned: May 1941–August 1941, 3rd
Flotilla (Kiel); August 1941–August 1943, 3rd
Flotilla (La Pallice)
Successes: Six ships sunk for a total of 19,323
tons, one ship of 6,207 tons damaged
Fate: Sunk 3 August 1943, northeast of Trinidad,
in position 11°35'N, 54°05'W, by bombs from
a PBM-3S Mariner of VP-205. 47 dead (entire
crew lost). Lieutenant (jg) C. C. Cox attacked
U-572 on the surface and was shot down during
the bomb run with the loss of all hands.
I have never read or heard of a U-boat being sunk or seriously damaged by strafing alone.
More documentation can be found at
www.history.navy.mil
Unfortunately the power of the .50 cal has been greatly exaggerated in popular media.