A (reserve fleet) may pertain-to a military-or-other-action-organization.
A fleet can be constituted-of-or-filled-with (fire engines).
A fleet can be constituted-of-or-filled-with some merchantmen.
A fleet can be constituted-of-or-filled-with (fuel tankers).
A fleet can be constituted-of-or-filled-with some minibuses.