Camouflage: by means of carvings in the cement.

On the outside:
trying to brake up the distinctive shape could be done by nailing old newspapers/empty cement bags/small wooden beams or patches of cloth into the sheet piling fine example of the use of carvings in the cement
On a R 621 Gruppenunterstand

photo: SBP

On a gunbunker M 272, La Pointeau near St Nazaire, F, 08-2005

photo: HA

an other example  

bunkers around Brest, Brittany, F

photo's: O

nice example, even the hooks for netting are very well kept! camouflageconcarvingsbud.jpg (34262 bytes) what a great sight! And what a view!

R669 Schartenstand für Feldgeschütze (60º) ohne Nebenräume, Port Louis, Südwall, F

photo: ER

R 636 command bunker , H.K.B. 17/976, Bud, Norway

photo: EE

fine example of the use of carvings in the cement camouflage on the outer walls probably achieved by using the paper bags
VF commandbunker, H.K.B. 24/978 Loshavn, N

photo: EE

'F Stand' O.K. 538, St.Pt.Gr. Blavand near Esbjerg, DK, 07-2001
the same effect on the standard casemate for coastal batteries and again on a gun bunker resulting in round patterns

Gun bunker R671 SK, 'M.K.B. Vineta' 4*15 cm, 'Festung Hoek van Holland', NL, 01-2001

Gunbunker R612 of the same battery
Festung Hoek van Holland, NL, 03-2002
and resulting in straight and round patterns ... and again...
On the same type of bunker R 612

St.Pt. XXXV H, Dintelse Sas, Dinteloord, NL, 05-2001

Gunbunker R612, Stp. V H , Festung Hoek van Holland, NL, 11-2004

an other nice example of nailing items into the sheet piling a nice pattern!
On a R501 Gruppenunterstand', 'W.N.' 316 LH, 'Stp.Gr.' Schouwen near Haamstede, NL, 07-2002

On a gunbunker R611, St. Pt. Hötzendorf, Westkapelle, NL, 04-2002

photo: LvdW

and a combination of the last two good example of the use of wooden beams, typical this kind of camo was used in the Dieppe region
On a gunbunker R669

St.Pt. XXXIV H, Willemstad, NL, 05-2001

On a bunker in Die 06, Dieppe, F, 1995

photo: SD

or what about this one? Looks like a snake to me!
Unfinished gunbunker 'M.K.B. Hamburg', 4*24 cm., Les Marettes near Cherbourg, F, 08-2001
or look at this pattern, very nice!
On a gunbunker 'R 680', Morsalines ('W.N' 109) near Cherbourg, F

photo: LvdW

On a groupbunker, 'R 502' Batterie Auderville-Laye, 2*20.3 cm. railway guns, Westeck Cherbourg, F, 08-2003

photo: LvdW

and again a nice pattern with small spots
or just making scratches, the result looks like if the bunker were made of 'Formsteine'

On a gun bunker 'R 612', Pointe de Saire Wn 115, east coast Cotentin Normandy, F, 08-2003

photo: LvdW

On a gunbunker 'R 669', Kerchaton near Lorient, 07-2004

well preserved!
On the inside: most likely the reason was not useless camouflage but an effort to absorb the sound when firing the gun inside the 'Kampfraum'.
the result of an empty bag of cement on the inside of the sheet piling ...

Inside a gunbunker 'R 612 Schartenstand für Lande- und Sturmabwehrgeschütze ohne Nebenraum', Btte. Cannevé, Normandy, F

photo's: PF

a swastika pattern?

r and l: Inside a gunbunker R 669, Batt. Emil, Cannevé, La Baule, Tu 47. m: Tu 49.

photo's: JFL l+m/HA r

nice examples!

l: Inside a gunbunker R 669, Batt. Adolf, La Baule, Tu 43. r: Inside a gunbunker R 625, Trescalan, La Baule, Tu 17, F, 08-2005

photo's: HA