Cutaway model of a WW2 British Mark 7 depth charge pistol together with its booster charge. The pistol is used in the depth charge Mk7 or Mk7 heavy.
The pistol is bronze made and consists of three main parts ; the setting head with the setting key and holes plate; the firing pin mechanism with detonator; the booster charge.
In top, the depth setting mechanism is placed. This mechanism is placed in a bronze housing. On top, a closing plate is screwed with the depth settings. In the centre a shaft is placed, over which the depth setting key is placed. The setting key is connected to a disc with different size holes , allowing water to enter the fuze (pict 09 , blue) with different speeds.
To the base of the setting mechanism a pipe is placed, connecting the setting mechanism with the firing pin mechanism bushing.
The firing pin mechanism is a closed bushing housing two steel discs which telescope over one another. These two discs fixate the spring loaded firing pin by pushing two balls inward in a recess in the firing pin. Between these two discs , a rubber bellow is placed which expands if water under pressure enters the bellow.
Setting depths are :
Safe = not arming
700 ft = 213 mtrs
140 ft = 43 mtrs
225 ft = 69 mtrs
385 ft = 117 mtrs
550 ft = 168 mtrs
300 ft = 91 mtrs
Functioning of the fuze:
After setting the key to the desired depth, the depth charge is launched by the projector. Upon entering the water, water starts entering the depth setting mechanism through the rectangular holes around the setting key (pict 08), passing through the filter grid (pict 06) and entering the space between the upper and lower fuze housing through one of the holes in the holes disc (pict 07) and the hole in the base of the depth setting mechanism housing (Pict 03, A). Depending upon the size of the hole the space between the depth setting housing and the firing pin housing fills with water fast either slow (pict 09 , blue). If the space is filled , water enters the firing pin housing (pict 04), starting to fill the rubber bellow though six radial drilled holes (B) on the outside of the firing pin housing. When the rubber bellow (C) expands from the inside out, is pushes apart the two discs(D&E), tensioning the firing pin spring (F) and allowing the balls (G) to move outward when the discs have moved apart sufficiently, releasing the firing pin (H) into the detonator (J).
The booster charge is placed loose from the detonator( pict 05, pict 09 green) , so if a detonator explodes by accident, it will not detonate the depth charge as the booster charge cannot be detonated. After the depth charge has entered the water, water pressure starts to push the booster charge over the detonator, allowing the depth charge to explode when the detonator is activated.
The fuze functioning is in fact time activated , by means of varying the hole size (pict 07) through which the fuze body fills with water. A large hole means the fuze body fills with water fast, exploding the depth charge at a shallow depth. A small hole means the fuze body fills with water slowly , allowing the depth charge to sink much deeper before exploding. It must be noted that the water runs in faster the deeper the depth charge has sunk, as the hydrostatic pressure mounts.
An advantage of this type of fuze is that it is not sensitive to pressure waves of other depth charges exploding in the vicinity as the fuze is not activated by a direct pressure wave on a bellow.
Length of the complete fuze with detonator : 397mm
Diameter of the fuze : 88mm
Length of the booster (w/o threaded part) : 117mm
Diameter of the booster : 86mm
Length of the complete fuze with booster (with treaded part) : 535mm
Regards, DJH
The pistol is bronze made and consists of three main parts ; the setting head with the setting key and holes plate; the firing pin mechanism with detonator; the booster charge.
In top, the depth setting mechanism is placed. This mechanism is placed in a bronze housing. On top, a closing plate is screwed with the depth settings. In the centre a shaft is placed, over which the depth setting key is placed. The setting key is connected to a disc with different size holes , allowing water to enter the fuze (pict 09 , blue) with different speeds.
To the base of the setting mechanism a pipe is placed, connecting the setting mechanism with the firing pin mechanism bushing.
The firing pin mechanism is a closed bushing housing two steel discs which telescope over one another. These two discs fixate the spring loaded firing pin by pushing two balls inward in a recess in the firing pin. Between these two discs , a rubber bellow is placed which expands if water under pressure enters the bellow.
Setting depths are :
Safe = not arming
700 ft = 213 mtrs
140 ft = 43 mtrs
225 ft = 69 mtrs
385 ft = 117 mtrs
550 ft = 168 mtrs
300 ft = 91 mtrs
Functioning of the fuze:
After setting the key to the desired depth, the depth charge is launched by the projector. Upon entering the water, water starts entering the depth setting mechanism through the rectangular holes around the setting key (pict 08), passing through the filter grid (pict 06) and entering the space between the upper and lower fuze housing through one of the holes in the holes disc (pict 07) and the hole in the base of the depth setting mechanism housing (Pict 03, A). Depending upon the size of the hole the space between the depth setting housing and the firing pin housing fills with water fast either slow (pict 09 , blue). If the space is filled , water enters the firing pin housing (pict 04), starting to fill the rubber bellow though six radial drilled holes (B) on the outside of the firing pin housing. When the rubber bellow (C) expands from the inside out, is pushes apart the two discs(D&E), tensioning the firing pin spring (F) and allowing the balls (G) to move outward when the discs have moved apart sufficiently, releasing the firing pin (H) into the detonator (J).
The booster charge is placed loose from the detonator( pict 05, pict 09 green) , so if a detonator explodes by accident, it will not detonate the depth charge as the booster charge cannot be detonated. After the depth charge has entered the water, water pressure starts to push the booster charge over the detonator, allowing the depth charge to explode when the detonator is activated.
The fuze functioning is in fact time activated , by means of varying the hole size (pict 07) through which the fuze body fills with water. A large hole means the fuze body fills with water fast, exploding the depth charge at a shallow depth. A small hole means the fuze body fills with water slowly , allowing the depth charge to sink much deeper before exploding. It must be noted that the water runs in faster the deeper the depth charge has sunk, as the hydrostatic pressure mounts.
An advantage of this type of fuze is that it is not sensitive to pressure waves of other depth charges exploding in the vicinity as the fuze is not activated by a direct pressure wave on a bellow.
Length of the complete fuze with detonator : 397mm
Diameter of the fuze : 88mm
Length of the booster (w/o threaded part) : 117mm
Diameter of the booster : 86mm
Length of the complete fuze with booster (with treaded part) : 535mm
Regards, DJH
Attachments
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01 - Mk7 depth charge fuze cutaway model.jpg -
02 - Mk7 depth charge fuze cutaway model backside.jpg -
03 - Mk7 depth charge fuze cutaway top part.jpg -
04 - Mk7 depth charge fuze cutaway model bellow & firing pin.jpg -
05 - Mk7 depth charge fuze cutaway model booster.jpg -
06 - Mk7 depth charge fuze cutaway model seting key and grid.jpg -
07 - Mk7 depth charge fuze cutaway model holes disc for depth setting.jpg -
08 - Mk7 depth charge fuze cutaway model setting key and depths.jpg -
09 - Mk7 depth charge fuze in depth charge.jpg -
10 - drum-type Mark VII depth charge onto the K-gun.jpg
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