Which Secondary Weapons are equip-able depends on the Soldier Class. This also includes 'Items' that are not strictly conventional weapons but fit the same item slot (e.g. Gremlin or Psi Amps).
What follows is a brief summary of weapons available and their relevant Soldier Class requirements.
Pistols[]
Pistols are a secondary weapon type restricted to the Sharpshooter Class.
Variants (Tiers)
Swords[]
Swords are a secondary weapon type restricted to the Ranger Class.
Variants (Tiers)
Grenade Launchers[]
Grenade Launchers are a secondary weapon type restricted to the Grenadier Class.
Variants (Tiers)
PSI Amp[]
PSI Amps are restricted to Psi Operatives.
Variants (Tiers)
Gremlins[]
The GREMLIN is restricted to Specialists.
Variants (Tiers)