Clue: Bitterness shown by Turkey abandoning Mediterranean port in campaign (9)
Answer: GALLIPOLI
Explanation: Definition: campaign
 GALL(bitterness/resentment) **plus**(shown by) [ "TR"(International Standardised Code for the country, Turkey) **deleted from**(abandoning) "Tripoli"(Mediterranean port in Lebanon or Libya, take your pick) ].
Defn: …/a series of military operations in the First World War, specifically in Turkey.