Dornier Do 18
Do 18G
Do 18 V4
Do 18D-0
A               V1, V3 and V5 for DLH
B               Project for a conversion kit between A and C (First project designs for the Do 18)
C               V2 and V4 military version
D-0           Military version , pre-production batch
D-1           Military version , first production version.  Two water rudders introduced during this series. Minor changes     in equipment led to D-2
D-2           Military version
D-3           Military version
E               Final designation for the civil Do 18 V3, V5, V6
F               Designation for the V7
G               Military version , Jumo 205D and improved armament
H               Dual control trainer without armament
J                At least 4 , the differens is unknown
N               Several sources mention this version but there are no documents that can verify this ( Kössler/Mohr)
W              The eighth D-3, Werk.Nr. 734 used for the World Record  for Long Distance
L                W rebuilt with BMW 132M engines