Try renaming the node that you are attaching the cargo to. I've compiled a list of what each label is used for by the game i.e. M## for main guns, A## for anti aircraft etc. Here's my list so far:
A= AA Gun
B= Bomb Payload
C= Radar RWR
D= Radio DF
E= Sub Emblem
F=
G= Broomstick node (?)
H= Hydrophone
I= Instrument (?)
J=
K= Cargo
L= Searchlight
M= Main Armament
N= Sonar
O= Sensor (Optical?)
P= Pilot/Sailor
Q= Signal Light (?)
R= Radar
RC= (?)
S= Secondary Weapon
T= Torpedo
U=
V=
W= ASW Weapon
X= Static Aircraft/Vehicle (?)
Y=
Z= Conning Tower
aud= audio
engine= engine sound
diesel= Diesel Engine Sound
electric= Electric Engine Sound
fore= Sound of bow wave
propeller= Sound of propellers
sink= Sinking Sound (?)
BLD= Bold Decoy Launcher
siaj= splash
b= Stern Splash (water above propeller)
C= Conning Tower Splash
F= Bow splash (right)
F01= Submarine bow splash (right)
F02= Submarine bow splash
F2 Bow splash (left)
ShipWake= Ship wake
SNK= Snorkel
TAR= Tarnmatte
TXR= External Texture