Many players like myself bury the mortar deep behind buildings. Brutes seem to have an especially hard time getting to them.
I use a 4 phase attack: 1. Send Brutes in on an axis of advance to get to the mortars with minimal damage or distraction - watch out for the Ship. Ships tend to attract Brutes out of proportion to their importance. Space the Brutes out - don't bunch them up. They'll bunch up when they get to their target. 2. As soon as the Brutes attract the attention of the first line of defensive weapons, send in Buccs on same axis of advance - widely spaced. 3. As the main attack progresses, more weapons get attracted to the Brute/Bucc onslaught. Then I send Gunners in, usually on an axis of advance perpendicular to the main attack - widely spaced. 4. If necessary, commit reserve force of 1 or 2 thieves or bombers (currently, I'm playing with bombers) - pick an axis of advance with no defensive weapons. A couple of hits and they're gone, but they do a lot of damage quickly if no one's shooting at them. Plus it's fun to watch them. With this attack, the Brutes keep driving into the middle of the defense because they're attracted to things shooting at them. The Buccs back them up and widen the breach by being attracted to nearby items. The Gunners stand off a bit, either behind the Buccs or to the side, and hammer resources and weapons attracted to the, by now, deeply penetrating Brute/Bucc intrusion. I prefer the Gunners attacking a flank because the defensive weapons waste time (thereby reducing shots) reorienting to widely separated attackers. If the defense is symmetric with no obvious attack axis, choose a corner away from the Ship. The goal is to take down the defensive weapon in the corner quickly and peel the defense open from the corner. If the defense looks too strong, hit the next button.
Definition: (DOD) A line of advance assigned for purposes of control, often a road or a group of roads, or a designated series of locations, extending in the direction of the enemy.
Sir Gangrene Beard has the definition exactly. Informally, think of it as a wide arrow (not a line) drawn on a map. Where you place the Brutes is the tail of the arrow with the head of the arrow pointed at the mortar. That's what you want them to do, but nothing's every easy. The Brutes will get distracted by weapons firing from the sides. [Watch out for the @##$%^^ Ship - it attracts Brutes like bees to honey.] You need to experiment with the number of each type based on your level. Currently, I using 4 Brute, 10 Buccs, 8 Gunners, 1 Bomber, and a Partridge in a Pear Tree. With experience, you'll be able to anticipate where the Brutes will get distracted and move away from the straight arrow. You'll then be able to see the axis of advance as a jointed or curvy line with an arrowhead pointed at the mortar.
An axis of advance (AoA) is for coordinating your own troops' movement. Movement along an AoA may confuse and confound the enemy, but the AoA is just "here's where I want you to go and basically how I want you to get there." An AoA isn't a route although it may be points along, say, a road. For example, a unit's AoA may be Road A meaning the unit is expected to move along Road A (but not necessarily on the road) and not on Road B. My apologies if the detail is excessive. I have it on good authority that I provide too much detail.
Right, but since there are no roads in this game, only beaches, I took your comment to mean along the beaches at multiple points with the purpose of sending them towards defenses and (by design) confuse the defense
The start of an AoA in this game is always "on the beach". The AoA's arrowhead is the intended destination; in this case, the mortar(s). You could have multiple AoAs; one for each group of attackers. If you separate the pirates widely enough on the beach, they'll naturally form separate groups each moving along a separate AoA. The mortars "pull" the Brutes to them by firing at the Brutes. So, since we want to kill the mortars, we take advantage of that attraction to fashion a plan to quickly (or massively, if you've got the troops) overwhelm the defenses on the way to the mortars. We think of the attack's AoAs starting at the beach and moving, like water flows downhill, toward the destination. We have to think about the distractions to the attackers and adjust the starting position to foster this downhill flow to the mortar(s). That mental image of the desired flow of each group of attackers to a destination is an AoA. My plan has two AoAs: one for the Brutes and Buccs and one for the Gunners. Unfortunately, we can't tell our attackers where the AoAs are but must rely on AI (Artificial Idiocy) to guide them. If we could give a group an AoA, two points would suffice: start point (on the beach) and end point (on the mortar). A more sophisticated AoA might add points in the middle to avoid, for example, getting sucked into engaging the @#$%^ Ship. [[The discerning and careful reader will no doubt deduce that a few of my attacks have have not gone as planned due to a Ship firing on my Brutes, the Brutes leaving the AoA to pound on the Ship, and my cherished Gunners and Buccs being slaughtered by the ignored mortar. Arghh!]]
Since a "picture is worth a thousand words", here's a picture with two AoAs. AoA 1 is the main attack and AoA2 is the flank attack by the Gunners. Notice the attack is on the side opposite the Ship.
I post mine to google plus, go to the image and choose download. It gives me an address to attach. Others use hosting sites like imugr and flickr