Shooting Script Bullet Doesnt Fire

I had a working script, then somewhere along the line something got deleted and I cannot figure out how to get back to where is was. I have a driveable tank with a game object attached to the end of the barrel that fires projectiles on a left mouse click. With the following script however, my bullets spawn but dont move. What have I miscalculated?

 using UnityEngine;
 using System.Collections;
 
 public class fireBullet : MonoBehaviour {
     
     public Rigidbody bullet;
     public float cannonPower;
     
     // Use this for initialization
     void Start () {
     
     }
     
     // Update is called once per frame
     void Update () {
         //fire cannon
         if(Input.GetButtonUp("Fire1")){
             
         //create projectile at location script is attached to
             Rigidbody instance = Instantiate(bullet, transform.position, transform.rotation) as Rigidbody;
         
         //add force to projectile
             Vector3 fwd = transform.TransformDirection(Vector3.forward);
             instance.AddForce(fwd*cannonPower);
             
         }
     }
 }