舰队 means "fleet" and refers to a group of warships or naval vessels operating together. It is used in military and historical contexts when discussing naval forces.
一支庞大的舰队正在向港口驶来。
yì zhī pángdà de jiànduì zhèngzài xiàng gǎngkǒu shǐ lái.
A massive fleet is heading toward the port.
这个国家的舰队在太平洋执行任务。
zhège guójiā de jiànduì zài tàipíngyáng zhíxíng rènwù.
This country's fleet is carrying out missions in the Pacific Ocean.
他在舰队里服役了整整十年。
tā zài jiànduì lǐ fúyì le zhěngzhěng shí nián.
He served in the fleet for a full ten years.