Hope my sense of scale isn't too awful this time......
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Tian Dan is the eighth and last vessel of the Cheng Kung class.
She was originally intended to be an advanced air defense development featuring the forerunner of the AN/SPY-1F radar, but as the materials had already been set aside for her despite the cancellation of this development, she was ultimately ordered to the same specification as the preceding ships (her Mk13 launcher is, IIRC, bought from the mothballed stock in the US).
This is also why she, unlike the rest of her class, doesn't have the 40mm L70 guns.
EDIT: Both ships have their Phalanx guns upgraded to the Block 1A.
Reference
HERE and
HERE (taken in 2019, but by 2019 there's already talk of upgrading all of the ROCN's Phalanx to Block 1B, so those 1A likely aren't a recent addition)