Type 904 shares the same hull of Type 991II Youdian class cable layer, but the original design encountered difficulty when the development of domestic Chinese saturation diving support system stalled. Decision was made to import such system from abroad, with French system eventually selected. Consequently, the original Type 904 never went into production because the design had to be modified to accommodate the foreign saturation diving support system, and the modified design is designated as Type 904I.
