Mortars are just a lighter weight version of artillery that can be transported much easier. Since they have to fire in an arch and suffer from the same shell travel delay as indirect firing artillery, they are effectively indirect firing artillery. ( although you can see the target directly )
That means they suffer practically the same drawbacks as indirect firing artillery. Indirect firing artillery works best on stationary ( not moving ) targets, such as flags, mg nests, field cannon positions, and other positions that cannot move. Indirect firing artillery can hit slow moving targets, but that takes quite some pratice/skill and a bit of luck.
If you want to effectively use mortars on the defence, you should use a lots of them firing at the same area at the same time. Only 1 mortar is practically useless to stop an advance, the weapon in itself is not a precission weapon.
Using mortars on the offence is much easier, when you use them as portable artillery to take stationary defenses under fire, surpressing them or killing them before an attack by infantry and tanks. ( people who actually do that are rare, but IRL it works that way, and in FH it could too )
D-Fensit works the same way as with grenades, hold the lmb to shoot shorter distances, how the hell it's even possible with a mortar though...
Thats is because the knee mortar is not a "true mortar". :) The allies thought it was a "knee mortar" and used it as such but its not such a great idea to do that because it will hurt alot. Its a grenade discharger. The japanese designed it to fill the gap between hand grenades and mortars. Its basicly saying a variety of the rifle grenade launcher. There where 2 types of dischargers the type 89 and the type 10. Im not sure but i think the one we got ingame is the type 89 discharger. Here's some more info about it. http://www.nps.gov/wapa/indepth/extContent/usmc/pcn-190-003117-00/sec5a.htm http://www3.plala.or.jp/takihome/grenade.htm#89GD
OT: Why cant you reload your rifle grenade? I dont mind if it takes 10 sec to reload, they're quite useful. The knee mortars never seem to work for me. one time I was in the palmtree "nest" on Guadalcanal and an american walks by like 20 feet away so I shoot at im and it lands like 3-4 feet aaway from him and he keeps walking...I ended up using my ariska on him. I find they work best to pop out when you get to a base, fire into a bunker or building and then put away. They do take some getting used to though, and you cant use them at all while running.
Mortars, espacially the knee mortar need to do more "weak" damage a heck of a lot farther. The knee mortar explosion should be at least a frag grenade. I imagine they would be cool in 8 man barages, fire all your rounds then charge the defenses. A mortar team and assault all in one. Now if only I wasn't the only assault class...
Lets take a minute to see how the mortar fires. Almost straight up, causing the shell to travel in a high arc (Picture the St. Louis arch) The idea is that the mortar can fire over obstacles such as walls or hills, allowing you to hit what conventional artillery cannot. To adjust the distance, I'll give another example, for aiming at something farther away. Angle the tube downwards a bit (pull down on the mouse until the reticle is lined up with the horizon, unless you're firing on an uneven surface, in which case you'll have to go by instinct), so that it's at an angle of, oh, lets say 45 degrees. The shell will travel a longer distance, but in a shortar arc. I hope this gave you guys an idea of how to use mortars. BTW, I once got an awesome mortar kill on Iwo Jima. A tank was attacking the airfield from the repair pad, and I was on top of the ridge with a mortar. I set up the mortar, took one look at the tank, used my sense of aim, and fired one shot. BOOM!!!. Dead on hit. hehehe. Oh, almost forgot. Do NOT set up a mortar with a roof over your head. Dumbest thing you can ever do in FH