So You Want To Be an OpCom?
Developing an effective scenario with an historical basis can take several re-writes and a lot of effort. Be patient and listen to senior members' advice.

Cimmerian operations always re-enact conflicts between well trained military units. Honorable warriors. The OpCom (Operation Commander) needs to start from an historical precedent and develop a scenario. Don't forget that you are not devising a competition to see which team is "better". You are designing a situation to simulate combat conditions and test the mettle of both sides, these are very different ends.  Keeping things "even" and having mechanisms in the scenario to control the flow of battle are important. The guys come out each month to have fun, so keeping the energy and enthusiasm of all the operators "up" is your responsibility.

What Not To Do
Cimmerian operations are never between the "good guys" and the evil baddies (you name it...rag tag bands of murders, mercinaries, prison inmates, druggies, hillbillies, fanatics, terrorists). These types of scenarios are inherently unstable and do not represent historical  military-combat by their very nature. We have seen that these types of scenarios usually degenerate and so avoid then with extreme prejudice. We also avoid the heinous "bad taste for its own sake" scenarios that are in fashion with other event producers and their less-mature customer base.

Historically-Based Scenarios

Tactical Withdrawal
This is an old standby Cimmerian scenario. It is used when bones are weary and energy is low, often as a way to finish a hard day of MilSim.
The Scenario:   The front line between Red Army and Blue Army has broken down. Blue Army is now in retreat. Blue Army has selected a small group of soldiers to slow Red Army advance long enough to give Blue Army a chance to reestablish a new defensive line.
The Operation:   Troops are divided into two groups with the attacking group having a 2 to 1 advantage. The goal for the attacker is to get have half of it's soldiers to the designated area before time is up. The defender's goal is to prevent this. This operation is usually conducted along a certain path or trail with a boundary usually set at 50 to 100 yards on both sides of the trail.
Possible Outcomes:   The Red Army completes its mission if it gets half its team to the designated area before mission time has elapsed. The Blue Army completes its mission if mission time expires before the Red Army completes its mission.
Tips:  Although the defenders lack the numbers, they have the constant advantage of setting up ambushes which usually give them a high kill ratio. As in real combat, this scenario works best for the defenders if they work in pairs. Be careful not to stay in one place too long and let the enemy bypass you. Remember, your mission is to delay the enemy onslaught.

Multiple Objective
This scenario is also a Cimmerian favorite.
The Scenario:   Variable.
The Operation:   Two armies are evenly divided. A number of objectives are secretly placed on the field in advance. The mission is for each side to control the specific objective called out by OpCom. This may require finding it using maps, compasses, radio direction finding equipment, or satellite navigation. At the end of each time period (usually one hour), the side in control of the objective has completed their mission and moves on to the next.

Downed Pilot
This scenario sometimes requires a person to assume the role of the downed pilot, but normally our loyal training dummy CPO Savage steps in.
The Scenario:  The Blue Army has lost a pilot behind enemy lines. Because of heavy enemy presence, a direct rescue is not feasible. A platoon of soldiers are sent in to rescue the pilot and move him to a designated LZ (Landing Zone) for extraction before the pilot is captured and too many enemy patrol show up. Time is of the essence!
The Operation:   There are two armies: the Blue Army (the rescue team) and the Red Army (the enemy patrol). Armies are divided with the Blue Army starting with a 2 to 1 advantage. 
The Mission:  The Blue Army's mission is to locate and rescue the pilot, and get him safely to the LZ for extraction. The goal for the Red Army is to locate the pilot and take him back to their base for interrogation.
Pilot Rules (Live Pilot):   Before the start of the mission, the pilot moves to the center of the field and finds a hiding spot out of view of both teams. He must remain there until he is found by one of the two armies. Once he is found, any soldier within 30 feet may give him a command. The pilot must follow any commands given to him. Should both Red and Blue soldiers be in the area, the pilot will obey the Blue soldier. If the pilot suddenly finds himself alone, he will seek the nearest hiding spot and wait until he is found again. To make things a little more realistic and difficult, a live pilot can pretend to have a wounded leg so the soldiers must assist or even carry him.
Pilot Rules (Dummy Pilot):   If a dummy is used, it will be hidden on the field by the OpCom team in advance. Once the dummy is found, any soldier can carry the dummy. Should the soldier or soldiers carrying the pilot get hit, the pilot is dropped at that spot. The pilot is then free for anyone else to recover. The pilot can not be killed. To make things a little more realistic and difficult, the dummy may be required to be carried on a stretcher.
Mission Completion:   The mission is completed when one of the armies get the pilot to their designated area.
Tips:  Begin by patrolling and spread out to cover more ground. Communication is key to keep track of the pilot's location.

Convoy
This scenario requires the use of one or more military vehicles. The OpCom should arrange in advance for the required vehicles to be brought to the area of operation.
The Scenario:   The mission objective for the Red Army is to get its vehicles from point "A" to point "B" in the designated time period. The mission objective of the Blue Army is to prevent this from occurring.
The Operation:   Soldiers are divided into two even armies. In some operations, the army with the vehicles may be given a numerical advantage. The Red Army can advance their vehicles only as far as their most forward soldier can. The vehicles are immune to small arms fire and may only be destroyed by a rocket launcher or mortar. Should the vehicle be destroyed, it simply halts for 5 minutes and then resumes its advance. All personnel in the vehicle are also killed.  For safety purposes, no vehicle can ever move faster than a quick walking pace. All soldiers must always be aware of the proximity of a vehicle, because the driver may not be able to see the solder.  Vehicles have a 25-foot safety zone just like a soldier, so never approach the vehicle closer than 25 feet.
Mission Completion:   The Blue Army completes its objective when it gets its vehicles to the designated area before mission time has elepsed. The Red Army completes its objective if mission time expires before the vehicles reach the designated area.
Tips:  This is usually a high action scenario. Make sure you have a lot of ammo and spare batteries.  

All Scenarios have a basic premise that come from an historical engagement or from sources in more recent history, such as:

A rear guard tactical withdrawal along a road or other similar feature, the defenders' objective to prevent the attackers from breaking through,

To capture and secure a tactically important position, then defend its perimeter until relieved,

To locate a downed pilot and rescue (or capture) the injured pilot, and recover important military intelligence located at the crash site,

To locate hidden enemy ammunition caches in their territory, and destroy the munitions in place,

To locate an enemy POW compound deep inside their territory, free friendly troops, and successfully return to friendly lines

New scenarios can be developed by the OpCom as long as they are based in some manner on historical military combat events.