Best timing
Tall Ships Festival (occasionally in spring/summer, check schedule) - Historic ships along the Thames, providing a great contrast with HMS Belfast.
D-Day Anniversary (June) - Special flags, banners, and sometimes gun salutes or reenactments.
Lord Mayor’s Show (November) - River pageant and illuminated boats near the Tower Bridge area.
Remembrance Day (November) - Wreaths, poppies, and ceremonies give the ship a solemn, powerful atmosphere.