Please help! WW2 U.S. Navy Mk1 Mod2-3???

[Tater]

Hello Collectors, and Thank You in advance!
I do apologize as this is my first post on your site but I have been lurking for a minute. Anyways, I’ve recently purchased what I believe to be a WW2 era U.S. Navy Mk1 Mod2 or 3. Unfortunately I cannot find any photographic evidence to support my claim. The original advertisement said it was “garage art” and not real ordnance but my gut said it was real.
https://militaryantiquesmuseum.com/zyo0001-postwar-trench-art-aerial-bomb-inert.25435.archive.htm
So my search began. I knew it looked like a WW1 bomb but other than that I hadn’t a clue? So I searched for info on WW1 bombs and found out it had more than a passing resemblance to a U.S. Mark 1 bomb but the added braces on the fins lead me to believe it was an interwar bomb (1919-1936) but there was absolutely zero info that I could find for U.S. ordnance during that period. My search ground to a halt...
Until I came across this image...

Yes, I know it’s a digitized image for a videogame or something but the little yellow bomb at the top looked a lot like my “garage art”. The bomb in the image was labeled as a U.S. Navy Mk1 Mod2 and that gave me hope.
So I started looking again and I came across something called a “modified Mark” series of bombs used by the U.S. Army during WW2 but they all had box fins...

But then I thought maybe the Navy did things a little bit different? And that led me to this...

Look at the fin construction on the Mk1 Mod2-3 but unfortunately there are no pictures...
Does anybody have more info than what I’ve shown here because this is absolutely everything that I could find?
Photographic evidence or even the differences between the Mod2 and 3 would be greatly appreciated!

 

[Dreamk]

100lb MkI Mod 2&3 (Navy) - Navy has "Mod"s - data on 1st pic, drawing on the right of 2nd pic (left is the later Navy 100lbs MkIV - pay attention they are not at the same scale, look at the data, the MkIV is shorter by 1/4 than the MkI)


100lb MkI MIV (Army "Mark" series) - Army has "M"s


The top yellow bomb 3D model on on the 1st pic on your post is indeed a tentative of reconstruction of the Navy 100lb MkI Mod 2-3 bomb, while the grey one under it is aimed at representing the Navy 100lb MkIV Mod 1-2.

The bomb on display in your link seems indeed to fit the Navy 100lbs MkI Mod 2-3.

 

[Tater]

Thank you, Dreamk!

 

[Tater]

Anybody have any photos of these?

 

[Dreamk]

The only photos I know of are of the similar USAAF MkI MII (not MkI M2) that saw very limited use, not being officially adopted, even as a limited standard or a reserve standard - here tested on a Martin Bomber B10 (all US B10 served with the USAAC, none with the Navy, so these are army bombs not navy ones) - other 100lbs army bombs of the various Mk models had only one reinforcing bar between fins (or not at all on earlier models).

and here under a Curtiss B-2 Condor bomber

The design of bomb fins was always a problem in US bombs development as they kept deforming during the fall - till the development of the "box" fin units that insured rigidity - this was developed and tested as early as 1931 but implemented only at the end of the decade.

 

[Tater]

Dreamk, maybe we cannot see the forest for the trees? I mean, maybe the explanation is right in front of us?
I had assumed that the “Mark series” bombs used by the U.S.A.A.C. were all of the “box fin” variety... BUT your photos proved that theory wrong! So by looking at all of the images that you and I have posted here... I believe that there is no difference in the bombs used by either the U.S.A.A.C or the U.S Navy. The difference is in the “Mod”. I believe all the “Mark1” bombs had the fins along the body until the “Mod4” which used the “box fins”... What do you think? Or am I missing something?

 

[Dreamk]

Tater, it's a little more complicated.
During the interwar period, the army bombs were only "improvements" on ww1 designs - based mostly on the French Gros-Andreau. These improvements included better metallurgical techniques, better fuzing, and strengthening the fins - generally using a single reinforcing strut for bombs up to 600lbs and 2 struts over that weight.
The Navy introduced and put in service a number of new bomb designs. This was so for obvious reasons - they had budget while the USAAC was running at a minimum. However the Army experimented new designs and test it at the Aberdeen proving Grounds, but did not produce new bombs till the end of the thirties. The 1931 model was adopted for production at the end of the decade as the 100lbs M31 HE bomb. It used a cylindrical design that has began to be implemented by the Navy already during the mid 20s, then successfully improved.
The need to do with what you have when there is no budget to produce new bombs, and the periodical changes in the structure of the USAAC bringing with them changes in designations (the well known "new broom effect" - no real change beyond the new name) led to a real mess that the following list may help to understand:

US Army bombs 1918-1936
1918-30
Mk I Drop 100lb
Mk II Drop 25 lb
Mk III Drop 50 lb
MkIV Drop 300lb
MkV Drop 600lb
MkVI Drop 1100lb


1930s
MkI series Demolition:
welded joints circumferential and longitudinal. tail fuze only (no arming vanes)
25lb (previously drop Mk II)
50lb (previously drop Mk IIII)
100lb
MkI MI series Demolition:
nose fuze with arming vanes (and for 300 and 600lb, tail fuze too with arming vanes)
Fins strengthening braces
100lb
300lb
600lb
MkIII series demolition:
both noze and tail fuzes with arming vanes
No longitudinal welds, only circumferential ones
Fins build at a single unit, with stengthening fin braces.
100lb (previously drop Mk I-C)
300lb (previously drop Mk IV-C)
600lb (previously drop Mk V-C)
1100lb (previously drop Mk VI-C)
Cylindrical body series:
Nose and tail fuzes with arming vanes
fina ssembly designed as a unit, with strenghtening braces.
2000lb Mk I,
2000lb MkI MI,
2000lb MkI MII


Standard production 1930
MkIII series demolition:
100lb MkIII
300lb MkIII
600lb MkIII
1100lb MkIII
2000lb MkI MII
Substitute standard for production
100lb MkI MI
300lb MkI MI
2000lb MkI MI
Obsolete (Training)
25lb Mk I
50lb Mk I
Limited standard (War reserve)
100 lb Mk I (previously drop Mk I)
600lb Mk I MI
2000lb Mk I


1930 Fragmentation
Standard production 1930
30lb M5 (ring type body)
Limited standard (War reserve)
17lb Mk II (previously fragmentation drop Mk II-A)
25lb Mk III (previously fragmentation drop Mk II-B)


1930 Dummy bombs (empty)
40 lb Incendiary Mk I
40 lb Incendiary Mk II
25 lb Demolition Mk I
50 lb Demolition Mk I
100 lb Demolition Mk I
300 lb Demolition Mk I


1930 Chemical
Nose fuzes only 9with vane for 30lb)
30 lb MI chemical
50ln Mk I demonstration

Bombs used in 1925 in the Billy Mitchell experiments - most are still basically ww1 bombs:

Bombs used by the navy in 1920s

US Navy practice bomb MarkVII from 1932


US Army 600lb bomb from 1923 - new fin shape

US Army prototype for 100lbs with modified fins from 1925

US Army prototype from 1931 of what will become the 100lb bomb M31


The 100lb MkI seems to have been an exception - a bomb common bomb (except fuzing) to the Army (under the designation MkI MII) and the Navy - probably in expectation of the new cylindrical 100lb bomb being produced under the designation MkIV