From Halopedia, the Halo wiki
Described as looking like an overstuffed or pregnant cigar with a large megaphone at the front, bladder ships are used to replenish the ammunition used for starship plasma weaponry. To do this, they have a large collection cone that sucks up a specific type of gas within a planet's atmosphere, which is then compressed and stored within a liquefied form for shipment. The cone is composed of eight flexible poles, with flexible webbing that connects it together. When not in use, it is retracted into the ship's bow. ONI analysts suspect that they are also equipment freighters that carry spare parts and raw materials for their fleet.
The bladder ship is unable to activate its shields when the cone is extended, which renders it vulnerable to infiltration or attack. To defend itself, it has several hangars for space fighters such as Elsedda-pattern Banshees and Seraphs.
In March 2526, three bladder ships traveling with Mjern-pattern agricultural support ship were left at Etalan to recover supplies for the Fleet of Inexorable Obedience. On March 26, the ships were destroyed by Blue, Green, and Gold Teams.
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