Question: What was the codename of the battle which almost destroyed Shuri Castle?

Context paragraphs:
Battle of Okinawa: The Battle of Okinawa (Japanese: 沖縄戦 , Hepburn: Okinawa-sen ) (Okinawan: 沖縄戦 , "Uchinaa ikusa " ), codenamed Operation Iceberg, was a major battle of the Pacific War fought on the island of Okinawa by United States Marine and Army forces against the Imperial Japanese Army and included the largest amphibious assault in the Pacific War during World War II, the April 1, 1945, invasion of Okinawa itself.  The 82-day battle lasted from April 1 until June 22, 1945.  After a long campaign of island hopping, the Allies were planning to use Okinawa, a large island only 340 mi away from mainland Japan, as a base for air operations for the planned invasion of the Japanese home islands.

Okinawa Shrine: Okinawa Shrine (沖縄神社 , Okinawa Jinja ) is a Shinto shrine in Naha, Okinawa, Japan.  Established at the end of the Taishō period on the site of Shuri Castle, the main hall of which was reused as the haiden (hall of worship), the shrine buildings were destroyed in May 1945 during the Battle of Okinawa.  Both castle and shrine have since been rebuilt while this phase has been written out of the "official history" currently told at Shurijō Castle Park.

Shuri Castle: Shuri Castle (首里城 , Shuri-jō ) is a Ryukyuan "gusuku" in Shuri, Okinawa.  Between 1429 and 1879, it was the palace of the Ryukyu Kingdom, before becoming largely neglected.  In 1945, during the Battle of Okinawa, it was almost completely destroyed.  After the war, the castle was re-purposed as a university campus.  Beginning in 1992, the central citadel and walls were largely reconstructed on the original site based on historical records, photographs, and memory.

Shuri Station: Shuri Station (首里駅 , Shuri-eki ) is a railway station on the Okinawa Monorail located in Naha, Okinawa Prefecture, Japan.  The station was originally planned to be named Tera Station (汀良駅), after the neighborhood within Shuri, but opened as Shuri Station on August 10, 2003.  It serves the center of downtown Shuri, Shuri Castle, and its environs.

Tamaudun: Tamaudun (玉陵 ) is one of the three royal mausoleums of the Ryukyu Kingdom, along with Urasoe yōdore at Urasoe Castle and Izena Tamaudun near Izena Castle in Izena, Okinawa.  The mausoleum is located in Shuri, Okinawa, and was built for Ryūkyūan royalty in 1501 by King Shō Shin, the third king of the Second Shō Dynasty a short distance from Shuri Castle.

Shikina-en: The gardens of Shikina-en (識名園 ) are located on a small hill to the south of Shuri Castle in Naha, Okinawa.  The residence and its gardens are also known as Shichina-nu-Udun (シチナヌウドゥン ) or Southern Gardens (南苑 ) , as opposed to the Eastern Gardens (東苑 ) or Uchayaudun (御茶屋御殿 ) , laid out on a small hill east of Shuri Castle in 1677.  In 1992 Hiroshi Shō, the great-grandson of Shō Tai, the last king of the Ryūkyū Kingdom, donated the royal mausoleum of Tamaudun and Shikina-en to the City of Naha.

Uni-Ufugusuku: Uni-Ufugusuku (鬼大城), or Ufugusuku Kenyu (大城賢雄) (fl.  15th century), was a martial arts master and Ryukyuan general who served the Ryukyu Kingdom.  "Uni" is an Okinawan cognate of the Japanese "oni," which means ogre.  He received this nickname because he was about 6 ft tall.  He was the personal attendant of King Shō Taikyū's daughter, and lived in Katsuren Castle when she married the Aji Amawari.  During the Aji's infamous grab for power in 1458, Ufugusuku took the King's daughter back to Shuri Castle.  He led the Ryūkyūan army to depose Amawari, and personally executed him.  He later became Aji of Goeku Magiri, residing in Chibana Castle, and married the king's daughter.  He was expelled after the First Shō Dynasty fell and later committed suicide.  His tomb is at Chibana Castle, in Chibana, Okinawa City, dug into the hillside next to his wife's tomb.

Shureimon: Shureimon (守礼門 ) is a gate in the Shuri neighborhood of Naha, the capital of Okinawa Prefecture, Japan.  It is the second of Shuri Castle's main gates.

Shuri, Okinawa: Shuri (首里 , Okinawan: "Sui" or "Shui") is a district of the city of Naha, Okinawa.  It was formerly a separate city in and of itself, and the royal capital of the Ryūkyū Kingdom.  A number of famous historical sites are located in Shuri, including Shuri Castle, the Shureimon gate, Sunuhyan-utaki (a sacred space of the native Ryukyuan religion), and royal mausoleum Tamaudun, all of which are designated World Heritage Sites by UNESCO.

List of Historic Sites of Japan (Okinawa): This list is of the Historic Sites of Japan located within the Prefecture of Okinawa.  Much of the heritage of the Ryūkyū Kingdom and Islands was destroyed during the Battle of Okinawa.  The mausoleum complex of Tamaudun, Shuri Castle, Katsuren Castle, Nakagusuku Castle, Nakijin Castle, Zakimi Castle, Sefa-utaki, and Sonohyan-utaki all form part of the UNESCO World Heritage Site Gusuku Sites and Related Properties of the Kingdom of Ryukyu.

Supporting paragraphs: Shuri Castle Battle of Okinawa
Answer: Operation Iceberg