A birthing tank containing the fetus of Sim in a nutrient solution
A birthing tank was a type of tank used to breed a clone.
In 2153, a birthing tank – filled with nutrient solution – was used in the final stages of developing a mimetic simbiot, in sickbay of Enterprise NX-01. When Doctor Phlox brought Captain Jonathan Archer into sickbay to see inside the birthing tank, the tank was initially covered by a sheet. Once the covering was removed by Phlox, Archer was able to view the birthing tank and its contents, which was the seemingly Human fetus of Sim. (ENT: "Similitude")
The term "birthing tank" comes from the final draft script of "Similitude". In that script, the tank was described as having Plexiglass walls and being shown "surrounded by an array of monitoring and life support systems," though no such array of equipment appears in the final version of "Similitude".