18-inch Mk.7 (450 mm)

18-inch Mk.7 deployed by the PT-3

Description

18-inch Mk.7 was an American lightweight torpedo developed by Bliss-Leavitt in 1911 as the first American torpedo used on submarines and surface vessels alike. By 1917 an airborne Mk.7 Type D variant was developed, but it has never seen serial production. Mk. 7 remained in service until the end of the World War 2, primarily on the O-type submarines.

Currently, the only vessel using the torpedo is the PT-3 torpedo boat. Due to the short range and relatively low speed, it's best used against barges rather than more mobile targets.

Vehicles equipped with this weapon

• PT-3

General info

Torpedo characteristics
Torpedo Mode	Mass (kg)	Maximum speed in water (km/h)	Travel distance (km)	Depth stroke (m)	Arming distance (m)	Explosive type	Explosive mass (kg)	TNT equivalent (kg)
No	720	59	3.65	1	50	TNT	93	93

Effective damage

With a 93 kg warhead the Mk. 7 can destroy any coastal vessel and a majority of a low-BR destroyers, larger vessels will require a hit directly on the magazines to achieve a kill, though ships equipped with a torpedo bulges might be completely immune to the weapon.

Comparison with analogues

The closest peer among US torpedoes is the Mk.8-3 C/D, a torpedo with nearly double the explosive mass, 15% slower speed (50 km/h instead of 59 km/h) and over triple the range, making it overall by far more versatile weapon.

The closest foreign equivalent would be the Japanese Type 44 No.2 which has a similar mass and same calibre, but a better speed, higher explosive mass and a slightly longer travel distance.

Name	Country of origin	Diameter (mm)	Mass (kg)	Explosive type	TNT equivalent (kg)	Max speed (km/h)	Max range (km)
12.75 inch Mark 44		324	235	HBX	54.4	56	5.49
12.75 inch Mark 46		324	235	TNT	44.5	91	7.30
18 inch Mark XII		450	702	TNT	176	74	1.37
18 inch Mark XV		450	817	Torpex	395.2	61	3.20
18 inch Type 38 No.2 B		450	663	Shimose	104.5	59	2.00
18-inch Mk.7		450	720	TNT	93	59	3.65
21 in Mk.8		533	1,252	TNT	146	50	9.14
21 inch Mark I		533	1,270	TNT	102	56	11.00
21 inch Mk.20 Bidder		533	821	TNT	89	37	11.00
21 inch Type 43 (1910)		533	1,187	Shimose	143	50	8.00
45-36NU		450	951	TNT	200	76	4.00
53-38		533	1,615	TNT	300	82	4.00
53-39		533	1,780	TNT	317	94	4.00
53-56		533	2,000	TNT	400	93	8.00
53-57		533	2,000	TNT	306	83	18.00
53-65		533	2,070	TNT	300	126	12.00
Bliss-Leavitt Mk.1		533	680	TNT	91	50	3.66
C/06D		450	810	TNT	122.6	50	5.90
G6c		533	1,008	TNT	160	50	5.00
G7		500	1,365	TNT	249.6	69	4.00
G7a		533	1,528	SW39a	358.4	81	6.00
H/8		600	2,160	SW39a	268.8	67	6.00
LT 1A/1		450	812	TNT	250	74	2.00
Mark 35		533	803	Torpex	196	50	13.71
Mk.8-3 C/D		533	1,373	TNT	174.2	50	12.35
Mk.13		569	884	TNT	178	56	5.21
Mk.15		533	1,559	TNT	224	83	5.50
Mk.16		533	1,766	Torpex	915.2	85	6.40
Mk.IV		533	1,454	TNT	234	65	7.30
Mk.IX		533	1,693	TNT	340	67	9.60
Mk.IX**		533	1,693	Torpex	587.2	76	10.00
Mk.V		533	1,736	TNT	305	74	4.57
Mk.VIII		533	1,566	TNT	327	84	4.57
1909R		450	716	TNT	144	61	2.00
Model 1919V		550	1,358	Picric acid	261.8	80	2.00
Model 1923DT		550	2,100	TNT	308	72	9.00
1926V		400	674	TNT	144	81	2.00
L3		550	910	TNT	200	46	5.00
Pattern 1910		450	665	TNT	100	54	3.00
Pattern 1912		450	810	TNT	100	80	2.00
R.G.F. Mark VI**		450	700	TNT	134	56	5.49
S.I.170/450X5,25		450	860	TNT	170	76	4.00
S.I.270		533	1,715	TNT	270	74	4.00
S.I. 250/533,4X7,5 Tipo A		533	1,781	TNT	250	76	4.00
S.I. 270/533,4X7,2 Tipo I		533	1,700	TNT	270	89	4.00
S.I. 270/533,4X7,2 Tipo M		533	1,715	TNT	270	93	4.00
S.I. 270/533X6.84 Tipo L		533	1,700	TNT	270	93	4.00
Seal DM2A1		533	1,370	TNT	250	61	20.00
SET-40		400	550	TNT	80	54	8.00
SET-53M		533	1,480	TNT	100	54	14.00
SET-65		533	1,740	TNT	205	74	16.00
SET-72		400	730	TNT	80	74	8.00
Type 2		450	1,000	Type 97	448	72	3.00
Type 6		533	1,432	Shimose	223.3	65	7.00
Type 8 No.2		610	2,362	Shimose	380.6	70	10.00
Type 43		450	663	Shimose	104.5	48	5.00
Type 44 No.2		450	750	Shimose	121	65	4.00
Type 54 model 3		533	1,600	TNT	100	44	6.00
Type 72 mod.1		533	1,760	TNT	300	120	10.00
Type 89		533	1,660	Type 97	384	83	5.50
Type 90		610	2,540	Type 97	480	85	7.00
Type 93 Model 1, Mod 2		610	2,700	Type 97	627.2	91	20.00
Type 93 Model 3		610	2,800	Type 97	998.4	91	15.00
W.200/450X5,75		450	930	TNT	200	81	3.00
Whitehead A 110/450		450	936	TNT	110	56	4.00

Usage in battles

Much like all lightweight torpedoes, it's best used against large, slow targets with no torpedo defense. When using it, one must remember about the minimum arming distance, which is 50 m, or triple the full length of the PT-3. When faced with multiple fast coastal vessels and no alternative targets, it's worth to just launch torpedoes in a general direction of the enemy vessels - sometimes lucky hits are the best one can hope for.

Pros and cons

Pros:

• Low mass

Cons:

• Low maximum range
• Relatively low speed
• Small explosive filler

History

The Mk. 7 was the first American steam-driven torpedo that could be used by both submarines and surface vessels alike. Designed in 1911, it was also the first American wet heater torpedo.

The exact calibre of the torpedo was 17.7 inch, or 450 mm, though in the US it was typically rounded to "18 inch". It carried the Mk 7 Mod 5 warhead with 326 pounds of either TNT or TPX and a Mk 3 Mod 1 contact fuse. Torpedo had two modes, a low-pressure for 3,500 yards (3.2 km) travel distance and a high-pressure for 6,000 yards (5.5 km).

During the WW1 it has seen use primarily on the American K, L, M, N and O class submarines. With the retiring of the last of the O-class in 1946, the Mk. 7 ended its 34 years of career in the US Navy.

Media

Excellent additions to the article would be video guides, screenshots from the game, and photos.

See also

Links to the articles on the War Thunder Wiki that you think will be useful for the reader, for example:

• reference to the article about the variant of the cannon/machine gun;
• references to approximate analogues by other nations and research trees.

External links

• [Wikipedia] Bliss-Leavitt Mark 7 torpedo
• [NavWeaps] Bliss-Leavitt 18" (45 cm) Mark 7
• [San Francisco Maritime National Park Association] E.W. Jolie, A Brief History of U.S. Navy Torpedo Development - Part 2: Detailed Description Of Torpedoes - Bliss-Leavitt Torpedo Mk7
• [Naval History and Heritage Command] Navy’s Use of Torpedoes